Illicit drug sale seems to be increasing in developing countries, but it has received little scientific interest from research workers and health planners. A study was carried out in the underprivileged suburbs of Dakar. 10 sellers selected on two markets and a street corner were observed during one week day each: 144 buyers were thus seen on the spot. Age and sex distribution reveals differentiation in customers' patterns: women are more present on markets while men usually buy on street corners; young children are often sent by their parents when the location of the sale is near the house. The closer the seller is to his clients, the more regular they are. This suggests a differential integration in social life. Pharmaceuticals are bought for symptomatic treatment, especially pain or fatigue (77%). Aspirin is part of 58% of drugs sold; antidiarrhoeals (mainly tetracycline) and antimalarials (4-aminoquinolines) represent 12% and 7% of sales, respectively. Prices are low, as pharmaceuticals are sold as individual tablets. Total cost of drugs thus sold by 102 sellers on the 13 main markets of Pikine is 100,000 $ per year - 11 times the Ministry of Public Health expenditure for pharmaceuticals in this area. Better accessibility to drugs in primary health care structures would give an alternative choice to populations and be more effective than mere repression against illicit sellers.