The evaluation of several derivatization procedures for the gas chromatographic analysis of selected anticancer pharmaceuticals (cyclophosphamide, iphosphamide, flutamide, chlorambucil, and melphalan) in the presence of tricyclic antidepressants was carried out. Among the methods, concerning trimethylsilylation, tert-butyldimethylsilylation, and methylation, the most useful was methylation using (trimethylsilyl)diazomethane (TMSD), which is a safe alternative for the common reaction with diazomethane. Most of the anticancer drugs were unstable during derivatization using silylating agents, while antidepressants were stable in all tested conditions. Melphalan was the only compound, for which the results of all tested procedures were not satisfying. The TMSD-based procedure was validated, giving the results possibly suitable for the screening purposes in contaminated environmental samples.