Evidence for a role for drugs of abuse in the development of chronic psychotic syndromes is scattered throughout 40 years of literature. Electrophysiological studies examining groups believed to have chronic drug-induced psychotic symptoms yielded interesting findings. To our knowledge, no studies directly compared schizophrenia patients whose drug use preceded and those whose drug use followed the onset of psychotic symptoms. Twenty-six schizophrenia patients and 10 healthy control subjects were recruited for the study. Based on the SCID interview, schizophrenia subjects were classified into a Psychosis First (Psy 1st) group (N=11), Drugs First (Drugs 1st; N=8), and No Drug Use (No Drugs; N=7). Schizophrenia subjects were administered the Positive and Negative Symptoms Scale (PANSS). The P300 evoked response and sensory gating were measured for all subjects. Despite the small sample sizes significant differences were found between the groups. Most significantly, the P300 amplitude was smallest in the Drugs 1st as compared to the No Drugs groups, while sensory gating deficit was worst in the Psy 1st group. The data suggest that significant clinical and electrophysiological differences between these groups can be identified. Further research to better define these differences seems warranted.