Four dipyrone metabolites (4-amino antipyrine, 4-acetyl amino antipyrine, 4-formyl amino antipyrine and 4-methyl amino antipyrine) were determined in wastewater collected in Budapest, Hungary from the influent and effluent sides of the North- and South Pest Wastewater Treatment Plants (WWTP) by liquid chromatography mass spectrometry after solid phase extraction. Moreover, wastewater samples collected from a WWTP working with fix bed biofilms placed in greenhouses in one suburban area of Budapest with a hospital, as sole activity, were also processed and analysed by the above-mentioned method. The concentration of 4-acetyl amino antipyrine was the highest among the metabolites determined in the water samples ranging from 0.27 to 5.72 μg dm− 3. The most persistent metabolite was 4-formyl amino antipyrine. By comparing the wastewater treatment efficiency in wintertime, the fixed bed biofilm wastewater treatment seemed to be more efficient than that of achieved in conventional WWTPs using activated sludge.