The purchase of antimicrobial agents in drugstores in a district in Manila. The Philippines was examined in order to determine how these agents might be used. Most antimicrobial agents are imported as bulk products and repackaged by a large number of small firms into 1491 different preparations including 206 marketed as combinations with other drugs. Antimicrobial agents accounted for 20.1% of all drug purchases. Purchases were made without prescription in 66.3% of 1608 transactions. Most of these were aminopenicillins or penicillins G or V (40.0%). The most common perceived indications were respiratory tract infections (20.2%), tuberculosis (8.8%), "prophylaxis" (8.6%) and gastrointestinal infection (8.3%). Almost 90% of purchases were for 10 or less capsules or tablets. The median number of units purchased was 3. Customers with written prescriptions purchased a mean of 8 while those who self-prescribed purchased a mean of 4 units (p = less than 0.05). We believe that these practices can provide only limited clinical efficacy and should favor emergence of resistant bacteria.