A method was developed for generating pesticide aerosols within the respirable particle size range of 0.3 to 3.0 micrometers. Analytical methods were established for determining pesticide concentrations in chamber air samples and in tissues. A unique chamber exposure system was developed that permitted the simultaneous exposure of four different groups of rats to four different concentrations of pesticide from a single generation source. Parathion, methyl parathion, Thimet, Guthion, and Azodrin were administered to rats by the oral, dermal, intravenous or inhalation routes, and the LD50s or LC50s were compared. Inhalation was the most toxic route of administration, followed by the intravenous, oral, and then dermal routes. Females were more sensitive than males to parathion and Thimet by all routes of administration. Azodrin was more toxic to females by the intravenous and oral routes, and Guthion was more toxic to females by dermal application. No correlation was found between mortality and cholinesterase inhibition or blood or liver pesticide content. No gross or histopathological lesions were identified that could be attributed to pesticide treatment. Timed-pregnant rats were exposed to vapors/aerosols of chloroform, ethylene thiourea, Thimet, Bromacil, and Simazine for 1 to 3 hours daily on days 7 through 14 of gestation. No dose-related terata were found in any of the studies.