To determine whether the free availability of antimicrobial agents leads to misuse through self-medication, a house-to-house semi-structured interview was held in three different socio-economic areas of Karachi, Pakistan. Of the 2348 households visited, 1342 (57%) participated; this included 9209 individuals. Three hundred and twenty-two (3.5%) had used one or more antimicrobial in the previous 4 weeks, equivalent to 43 agents per 1000 persons per month. The most frequently used agents were amoxycillin (16.7%), co-trimoxazole (15.7%), erythromycin (10.9%), ampicillin/cloxacillin (Ampiclox, 9.1%) and metronidazole (4.5%). Of these, 91.4% were prescribed by a physician, 2.3% were advised by a chemist and 6.3% were used as self-medication. Self-medication increased with socio-economic status. High levels of resistance were found to ampicillin, co-trimoxazole, chloramphenicol and erythromycin. If these high resistance levels are related to the high frequency of antimicrobial use, over-the-counter availability cannot be held responsible. Education of the medical profession seems to be the single most important tool to control misuse of antimicrobial agents. Innovative approaches for continuous medical education are urgently needed.