These studies assessed the neurotoxic potential of N-methyl-1-(4-methoxyphenyl)-2-aminopropane (para-methoxymethamphetamine; PMMA), an amphetamine analog that has surfaced in the illicit drug market. Repeated subcutaneous injections of PMMA caused lasting, dose-related reductions in regional brain concentrations of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), and in the density of [3H]paroxetine-labelled 5-HT uptake sites. Comparison of the neurotoxic potential of PMMA to that of para-methoxyamphetamine (PMA) and 3,4-methyl-enedioxymethamphetamine (MDMA) showed that equivalent doses of PMMA and PMA (80 mg/kg) produced comparable depletions of 5-HT, but that these depletions were not as pronounced as those induced by a lower dose of MDMA (20 mg/kg). Striatal DA was not affected on a long-term basis by any of the ring-substituted amphetamines evaluated in this study. These data suggest that PMMA, like PMA and MDMA, produces long-term (possibly neurotoxic) effects on brain serotonin neurons, but that PMMA is less potent than MDMA as a 5-HT neurotoxin. Further, they raise concern over the illicit use of PMMA since humans could be more sensitive than rodents to the 5-HT neurotoxic effects of PMMA and related drugs.