Ruling highlights the need to demonstrate actual prejudice before technical evidence is invalidated

The Third Panel of Brazil’s Superior Court of Justice (STJ) examined whether the absence of technical assistants during certain stages of DNA testing was sufficient to invalidate expert evidence and require a new examination.

In Special Appeal No. 2,271,376/GO, decided on October 6, 2026, the dispute involved the lack of prior notice allowing technical assistants to monitor laboratory analyses and the opening of seals containing genetic material.

By majority vote, the Third Panel denied the appeal. Justice Daniela Teixeira dissented.

The underlying dispute involved an inheritance claim combined with recognition of a grandparent-grandchild relationship, in which genetic evidence had potential succession consequences.

A procedural irregularity does not automatically invalidate expert evidence

The ruling highlights an important distinction between a procedural irregularity and an actual violation of the right to a full and fair defense.

According to the STJ’s established case law, judges are responsible for assessing the evidence necessary to decide a dispute and may refuse additional evidentiary measures when the existing record is considered sufficient, provided that the decision is properly reasoned.

Therefore, an irregularity during the production of technical evidence does not necessarily require the entire examination to be invalidated.

The relevant question is whether the irregularity materially impaired the parties’ ability to challenge, monitor or assess the reliability of the evidence.

Technical assistants retain the right to monitor expert examinations

The decision does not eliminate the procedural role of technical assistants.

Article 466(2) of Brazil’s Code of Civil Procedure requires court-appointed experts to provide the parties’ technical assistants with access to and the opportunity to monitor examinations and expert activities, subject to prior notice recorded in the case file.

The STJ decision should therefore be understood as addressing the consequences of an irregularity in a specific case rather than eliminating this statutory right.

Demonstrating actual prejudice becomes particularly important

When challenging expert evidence, parties should identify how the alleged irregularity affected the reliability of the examination or their ability to exercise procedural rights.

Relevant questions may include:

• Which stage could not be monitored?
• Which technical procedure was not independently assessed?
• Was there uncertainty regarding sample identification or handling?
• Could the methodology be challenged?
• Were relevant technical questions prevented?
• Was traceability of the material affected?
• Could the irregularity have influenced the conclusion?

This approach is particularly relevant when scientific evidence plays a decisive role in litigation.

Relevance for family and succession disputes

DNA evidence can be particularly significant in proceedings involving parentage, ancestry, inheritance rights and other family relationships.

Such cases may have both personal and substantial financial consequences.

For this reason, technical monitoring should be considered part of the litigation strategy from the beginning of the evidentiary phase rather than only after an unfavorable report has been issued.

The decision may also inform other expert evidence disputes

Although the case involved DNA testing, the discussion surrounding actual prejudice may be relevant to other forms of expert evidence, including accounting, medical, engineering, environmental and technological examinations.

In complex disputes, legal strategy and specialized technical support should be coordinated to ensure that potential evidentiary issues are identified and documented at the appropriate stage.

PDK Advogados monitors developments in Brazilian family and succession law, litigation and complex evidentiary matters.

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