Cocaine has recently been shown to affect the outcome of pregnancy when taken by pregnant women. The authors measured fetal concentrations of cocaine and benzoylecgonine and reviewed autopsy and historical data for 62 successive infants who died at less than two days of age and were seen at the Los Angeles County Office of the Chief Medical Examiner-Coroner. Of 43 infants without an obvious cause of death at autopsy, cocaine or benzoylecgonine or both were present in 40%. None of the parameters studied predicted which infants would show cocaine or benzoylecgonine. We conclude that cocaine and benzoylecgonine concentrations should be measured on all infants who die at less than two days of age when the cause of death is not evident at gross autopsy.