Introduction: Acute poisoning represents a state in which a physician's rapid reaction is necessary to timely apply the right therapy. As the state of acute intoxication is frequently nonspecific by symptoms and patients are often unconscious, a rapid toxicological analysis is needed. Adequate samples should be used for the analysis, which will give the most information about the taken substance, particularly about urine and blood. Immunoassays are fast and easy to use, but require verification by a more accurate method. Although the GC-MS method is more demanding and an analyst’s expertise is needed, it is still considered to be the most reliable for toxicological testing. Objective: The objective of this research is to compare the results of toxicological immunoassay screening with the GC-MS analysis results and to estimate advantages and disadvantages of the two methods. Materials and methods: This cross-sectional research used urine and blood (serum) samples of 23 patients aged 42 on average admitted in the emergency department due to suspected acute poisoning over a period of 2 months. The urine sample analysis was performed by the EMIT method on Siemens EMIT Viva E automated analyser and by the GC-MS method on GCMS-QP2010 (Shimatzu, Japan) appliance after a prior preparation of the urine sample by liquid-liquid extraction. Results: Out of 23 patients tested in total, only 6 of them had a finding obtained by the immunochemical method consistent with the results obtained by the GC-MS method. 8 findings were false positive and 2 false negative. In addition, 16 patients had substances that cannot be detected by immunoassay. Conclusion: Immunoassay is suitable for toxicological screening, but it is not specific enough and is subject to false positive results, so the results must be additionally confirmed by a more reliable method such as the GC-MS method.