Monitoring trough levels of the drug and antibodies to the drug is important when patients with inflammatory bowel disease are treated with anti-TNF biological drugs, because it can help to guide therapeutic decisions. In our research we compared two commercial assays for measuring trough level of infliximab (TL IFX) – test Lisa-Tracker Duo Infliximab (Lisa-Tracker) and test apDia Infliximab ELISA (apDia). We compared our results to in-house developed ELISA test from University of Leuven (UHL). Linear correlations (Pearson R) between tests were R = 0,92 (UHL and apDia), R = 0,91 (apDia and Lisa-Tracker) and R = 0,89 (UHL and Lisa-Tracker). Our results indicate that TL IFX, meassured with three different assays correlate with concentration of C-reactive protein. Higher TL IFX, measured with UHL and Lisa-Tracker also correlate with endoscopic remission of disease. We showed that detectable TL IFX lead to continuation of the treatment with IFX. In our research we measured antibodies to infliximab (ATI) with commercial test Lisa-Tracker and compared our results with in-house developed ELISA test – UHL. Because of a lack of standardization among assays for ATI determination, we can only compare results qualitative. We found out that the absence of ATI, measured with both assays leads to continuation of treatment with IFX. When determinating predictors for high TL IFX in the future, the absence of ATI (determinated with UHL) was found out to be a good predictor for detectable TL IFX in the future.