Estimates of antibiotic availability from a number of countries throughout the world were developed as an indicator of potential patterns of human antibiotic use. Data were organized by major classes of antibiotics and by some individual products and converted to units of weight and defined daily dosages per 1,000 population per day. Estimates were based either on sales or on production and trade data, including global production of penicillins, cephalosporins, tetracyclines, and erythromycins. The data obtained showed that antibiotic availability can vary widely among countries as well as from year to year in the same country.