Thirteen patients displayed neurologic complications of intravenous abuse of "T's and Blues" (pentazocine and tripelennamine). In six, the major presentation was seizures. Three patients had strokes, and three had CNS infections, two fungal and one related to subacute bacterial endocarditis. One patient had hepatic failure and an unusual encephalopathy. Foreign body embolization is common; the materials enter the cerebral circulation because of pulmonary arteriovenous shunts. Emboli may cause seizures, which also occur as a toxic effect of the drugs. Infection is due to unsterile injections. Enzyme elevations and diffuse vasculopathy raise the possibility of immune mechanisms.