AbstractThe pharmacokinetics of HI‐6 were studied following intravenous administration to beagle dogs (n = 7). The bioavailability of two different strength intramuscularly administered doses was also determined in the same animals. After a 20 mg kg−1 intravenous dose, the mean (±S.D.) initial HI‐6 plasma concentration was 93·1 ± 10·μg ml−1. The mean half‐life was 48·2±17·7 min, the mean total body clearance was 5·16 ± 0·81 ml min−1 kg−1, the mean apparent volume of distribution was 0·37·0±20 1 kg−1 and 61·2±14·6 per cent of the dose was excreted as unchanged drug. The pharmacokinetic constants calculated following the 20 mg kg−1 intramuscular doses of 250 and 25 mg ml−1 solutions were not significantly different from those obtained following the intravenous dose. Also, the areas under the plasma concentration versus time curves were not significantly different indicating 100 per cent bioavailability from the intramuscular route of administration.