The state of California conducted aerial applications of malathion (MA) bait over urban areas in the southern California air basin in order to eradicate the Mediterranean Fruit Fly (Ceratitis capitata). Concern about the potential human health effects of this activity prompted a risk assessment conducted by the California Department of Health Services. Estimates of potential human exposures to MA and its primary breakdown product, malaoxon, (MO) are based on assumptions of daily human activities which influence the rate of contact with MA and MO. Several exposure scenarios, representing a range of activity levels from sedentary to very active, are used as surrogates for a variety of human activities. For each exposure scenario, acute dose rates are calculated using both the mean and the mean plus 2 standard deviations (SD) (98% upper confidence limit (UCL)) of measured environmental values. Chronic dose rates are calculated using long-term averages incorporating degradation and multiple applications at 14 day intervals, and the estimated 98% UCL for these averages. Based on this model, estimated adult dermal doses (1-246 micrograms/kg-d) are up to about 2000-fold higher than the estimated inhalation doses (0.01-0.1 microgram/kg-d) but are comparable to the doses from ingestion of contaminated unwashed backyard vegetables (30-80 micrograms/kg-d). For the individual who does not consume backyard vegetables, therefore, almost the whole dose of MA or MO would be due to contacting contaminated surfaces with skin.