The annual overall consumption of antibacterial drugs in Norway, categorized into human use, use in domestic animals and in farmed fish, was estimated from wholesaler and feed-mill sales statistics. Comprehensive data on drug consumption in human medicine in Norway are published on a regular basis on behalf of the drug authorities. These data, including use of antibacterial drugs, are expressed as the number of defined daily doses (DDD)/1000 inhabitants/year. DDD cannot be employed to compare antibiotic consumption in human and veterinary medicine as it is possible to calculate such data for only a few veterinary drugs. The only parameter for which data are generally available, so far, is the amount used in kilograms of active substance, which is the unit of measurement chosen in this study. It was found that annual overall sales of antibacterial drugs in Norway, including antibacterial and ionophore feed additives, decreased from 77 tonnes in 1992 to 49 tonnes in 1996, a 37% reduction. The use in 1996 in human medicine, animals and farmed fish was 35 tonnes, 13 tonnes and 1 tonne, respectively. While the annual amounts used in human medicine remained unchanged from 1992 to 1996, therapeutic use in fish farming declined by 96%. In domestic animals, therapeutic use and use as feed additives declined by 17% and 5%, respectively. During the study period, the size of the human and domestic animal populations at risk remained almost constant, while the biomass (weight) of farmed fish at risk increased by > 100%. This implies that both the absolute and relative consumption of antibacterial drugs in Norway decreased substantially during the study period. The use of antibacterial drugs, both in humans and in domestic animals, has changed in favour of penicillins, this being in accordance with general recommendations. The reduction in the use of antibacterial drugs in farmed fish has been almost solely due to the introduction of oil-adjuvanted vaccines against furuncolosis. It is concluded that the decline in the amount of antibacterial drugs used in domestic animals, and the changes with regard to choice of drugs, could be mainly attributed to changes in prescribing behaviour following advice and recommendations. Moreover, the overall use of antibacterial drugs in Norway is very low compared with that in most other countries and has been significantly reduced during the 1990s.