-Four replicated experiments were conducted to determine the concentration of oxytetracycline hydrochloride (OTC) in honey bee (Apis mellifera) larvae following application of the antibiotic to honey bee colonies. In the first experiment, the mean OTC concentration was significantly greater in whole larvae than in larval guts sampled from hives on the day immediately following treatment. In two further experiments, 0.3 g, 0.5 g and 1.0 g active OTC in caster sugar was administered to single-and double-storey colonies. The mean OTC concentration was above the minimum inhibitory concentration of OTC to Melissococcus pluton for 2 to 6 days post-treatment, depending upon the dose. The daily rate of change of concentration of OTC in larvae sampled from treated colonies ranged from 0.423 to 0.672. In a fourth experiment, application of 0.3 g and 0.5 g OTC in distilled water gave equal to or higher OTC levels in larvae on the first two days post-treatment when compared to the same doses applied in caster sugar. oxytetracycline hydrochloride / antibiotic / honey bee / European foulbrood / Australia