Chlorpromazine, chlorpheniramine, chloroquine, dimethylaminoethyl p-chlorophenoxyacetate, aspirin and acet-aminophen were individually administered at one or more dosage levels, to groups of female C57BL/6J mice from an average age of 10 months to the end of life. Each of the drugs are known or suspected stabilizers of cellular membranes. Except for two cases of apparently toxic effects, differences in life span between drug-treated animals and control animals were not significant at the p < 0.05 level. Dimethylaminoethyl p-chlorophenoxyacetate, which had previously extended the life span of male Swiss Webster albino mice by 27.3% of the period of administration (p = 0.039), produced a modest and not quite significant 5.9% extension (p = 0.077). Weight changes were negligible up to 19 months of age, but several of the drug-treated groups averaged somewhat lighter in weight than control mice by 25 months of age.