Abuse of alcohol has been found to be an important risk factor for fractures and osteoporosis, and tissue culture experiments have indicated that low concentrations of ethanol can affect bone formation and resorption. This study investigated direct effects of ethanol on bone cells using an in vitro resorption assay. Osteoclasts from long bones of 19-day prehatch chicks were seeded onto slices of dentine and cultured with control medium alone, or medium containing 0.001%, 0.01% or 0.1% ethanol, at 37 degrees C with 5% CO2 for 24 h before being removed. The volumes and areas of resorption pits made in the dentine were measured using confocal laser reflection microscopy (Lasertech 1LM21 system) and the pits counted. An increase in the pit numbers and mean pit areas, volumes and volume/area ratios was observed with 0.001% and 0.01% ethanol, with a dose-related, bell-shaped curve of resorption. Greatest mean volume resorbed per pit (p < 0.05), mean area resorbed per pit (p < 0.01) and number of pits was at 0.01% ethanol. Volume/area (mean depth) per pit was greatest at 0.001% ethanol (p < 0.05). This study has shown that ethanol, even at blood concentrations experienced by the social drinker, has an immediate direct effect on bone cells in vitro, resulting in increased resorption by osteoclasts.