The data obtained indicate that ELISA can be a valuable tool in screening skeletal tissue samples for drugs of abuse. Also, marrow may act as a significant depot for ketamine, as has been previously indicated for a number of other drugs. These preliminary findings indicate that epiphysis bone fragments may provide a more reliable and sensitive sampling site than diaphyseal bone from the mid-femoral region for studies of ketamine disposition in skeletal tissues. The percentage of decrease in absorbance varied significantly between different tissues examined under a given dose condition and generally decreased for marrow, epiphysis bone, and diaphyseal bone, in that order, at all dose levels examined. Measured sensitivity values for marrow, epiphyseal bone, and diaphyseal bone were 100 percent, 77 percent, and 23 percent, respectively (75 mg/kg dose). These results suggest that the type of skeletal tissue samples and position sampled within a given bone (diaphyses versus epiphyses) are important parameters in drug screening of skeletal tissues. The effects of various environmental factors (e.g., burial, humidity, and temperature) were not examined, but will be addressed in future research. For this study, 18 rats received 0, 15, 30, or 75 mg/kg ketamine hydrochloride acutely and were then euthanized within 15 minutes or 1 hour. Ketamine was extracted from ground femoral bone by methanolic incubation followed by liquid-liquid extraction (LLE); marrow was homogenized in alkaline solution, followed by LLE. Extracts were analyzed by ELISA and subsequently by GC-ECD. The effect of tissue type on the immunoassay response was examined through determination of binary classification test sensitivity and measurement of the relative decrease in absorbance in each tissue type. 2 tables, 6 figures, and 23 references