The purpose of this study was to determine the applicability of the serum osmolality in cases of intoxication with drugs or other substances. Twenty-one patients with ethanol intoxication, five with isopropanol intoxication, and 28 overdosed with 18 drugs were studied. Serum osmolalities and appropriate drug analyses were performed in all cases. The normal serum delta osmolality (∆osm) was determined in 56 healthy individuals. It was concluded that the serum ∆osm is an effective screening procedure for a group of intoxicants that attain high, toxic, serum levels and have relatively low molecular weights. This group includes ethanol, isopropanol, methanol, acetone, ethyl ether, and trichloroethane. In addition, if these intoxicants are identified the serum concentrations can be calculated. However, most drugs or intoxicants cannot be screened using the ∆osm because their serum levels are low and their molecular weights high, so that they have negligible effects on osmolality.