Experimental groups of rats were maintained at the LETC North Site retort building for periods of 5 to 8 days during four separate burns of the ten-ton retort. The oil shale used in all four retort tests was from the DOE Anvil Points Mine near Rifle, Colorado and contained 23 - 2 gallons of oil per ton. Two control groups of animals were housed in the animal care facilities. One group was subjected to similar physical conditions (temperature, sound, lighting) as those experienced by experimental animals in the retort building while the other control group was maintained under standard animal care facility conditions. Blood and tissue samples were taken from most animals the same day the exposures were terminated although some animals were sampled at periods of 1 to 3 weeks after exposure, to see if the effects were reversible. A detailed toxicological screening procedure which included numerous biochemical, physiological and histopathological measurements was used to evaluate the effects of the exposures. Experimental groups of rats maintained in the retort building showed changes in liver function, serum enzymes and catecholamines, some histological alterations, and, for rats exposed during pregnancy, possible adverse fetal effects. The magnitude of these changes varied with the different retort tests. However, control rats maintained under simulated physical environments also showed a few biochemical and developmental effects that were similar to those of experimental animals indicating the contribution of physical factors to some of the changes. Together, the results indicate that the experimental design and toxicological screening procedures used in these studies provide a relatively inexpensive and simple approach for prediction of potential health risks to animals, including man.