The application of medicinal plants as a mechanism of cure, prevention and treatment of diseases has increased significantly in recent years. Several substances can also cause adverse effects and toxicity, lead to analytical interferences in laboratory tests. This study aimed to evaluate the in vitro analytical interference caused by the application of crude ethanol extract from leaves of Aspidosperma macrocarpum in colorimetric tests. To this, were added increasing concentrations of the extract to the reaction medium on the biochemical determination. These measurements were perform with diagnostic kits and tests were conduct according to manufacturer's recommendations. According to the results, the crude ethanolic extract of leaves of Aspidosperma macrocarpum may cause analytical interference in vitro in the colorimetric determinations of glucose, cholesterol, triglycerides and urea.