With computerised data on drug prescriptions, which were collected among a sample of 362 internist, general and medical practitioners throughout Germany, the effects of the drug budget, based on the German Health Care Structure Reform Act (GSG), on diabetic patients were analysed. The data of 3053 diabetic patients (10% random sample) were compared with the same number of nondiabetic patients for the period of July 1992 to December 1994. The frequency of consultations per patient increased in both groups during the study period (p < 0.01). Diabetic patients had more contacts with the physicians than nondiabetic subjects (p < 0.01). The prescriptions and costs among the patients with diabetes decreased in the first six month of 1993 (-10%/ -16%). In the following time costs increased and exceeded the values of 1992 by about 13%. The costs per prescription decreased during the study period about 10%. The data show that costs as well as prescriptions per consultation between diabetic and nondiabetic patients remained in the same ratio. The proportion of consultations with > or = 1 prescription increased in diabetic patients after the GSG. A refusal to prescribe drugs in primary health care practices among diabetic patients was not observed. There was also no restriction on prescription drug use among diabetic patients compared with nondiabetics.