A solid dosage form for multiple use was developed for parenteral administration of diacetylmorphine in a clinical trial on co-prescription of heroin to heroin addicts. A 300-mg/mL diacetylmorphine hydrochloride solution was lyophilised as 10-mL aliquots in 30-mL glass vials, to be reconstituted to 150 mg/mL with water for injection before use. Addition of bulking agents for improvement of the cake structure of the lyophilised product appeared unnecessary. Stability studies indicated good stability of the lyophilised product under prescribed storage conditions (25 degrees C, 60% relative humidity) and under more extreme conditions (40 degrees C, 75% relative humidity). The reconstituted product was found to be stable for six days at room temperature. Suitability of the product for multiple use was supported by the fact that the reconstituted product was found to be antimicrobially active.