In a comprehensive study on the fate of amitriptyline (At, Laroxyl) in depressive patients, it was investigated whether their compliance could be controlled in analysing the concentration of riboflavin (vitamin B2) in urine. Therefore, they were medicated for 3 weeks with special tablets (Ro 4-1575/063) containing 150 mg At and 15 mg riboflavin. Different modalities or urine samplings were designed in order to establish the optimal conditions for testing compliance. Riboflavin, creatinine, At and nortriptyline were measured in urine, the tricyclic drugs also in plasma. The results show that compliance could be tested in analysing urine before and 4 h after the intake of the drug. However, this design was associated with a considerable subjective constraint for the patient.