OBJECTIVE To evaluate the effect of introduction of treatment and sterilization guidelines on the number of avoidable injections and on the sterility of needles and syringes. METHODS In 1991, 66 randomly selected health units in Mwanza Region, Tanzania, were visited and factors were determined that might contribute to HIV transmission by injections. In a workshop with all senior health workers from the region, findings were presented and treatment and sterilization guidelines developed. Thereafter, seminars were held at each health centre of the region. Four months after the intervention, data were collected at the same health facilities in order to assess changes in prescribing practices, sterilization procedures, and sterility of needles and syringes. RESULTS The knowledge on indications for injections improved markedly for paramedical staff. The proportion of outpatients receiving an injection dropped from 23% to 10% and the proportion of patients receiving an avoidable injection dropped from 16% to 6%. Procedures for sterilization, keeping sterilized equipment, and administration of injections improved. A smaller proportion of sterilized needles and syringes tended to be contaminated in dispensaries, but this reduction from 44% to 22% was not significant. CONCLUSION Considerable improvement in knowledge, prescription practices and sterility procedures was observed at dispensary level after carrying out a training programme.