This study examines the effect of ibuprofen on the toxicity produced in mice by the anticancer drug, doxorubicin. Ibuprofen solution made in 0.02% sodium carbonate, was administered subcutaneously in doses ranging from 10 to 40 mg/kg/day. Sodium carbonate served as a vehicle control and saline was used as a reference control. Treatment with saline, sodium carbonate, or a specific dose of ibuprofen began two days before administration of a single intraperitoneal dose of doxorubicin 17, 20 or 25 mg/kg and then continued for the next thirty days. Mortality was followed for thirty days. The analysis of the data by the Litchfield and Wilcoxon method revealed that there was neither a difference in doxorubicin LD₅₀ values not in the potency ratios between saline and any dose of ibuprofen treatment. Treatments with sodium carbonate and ibuprofen at 30 mg/kg/day offered slight protection over saline treatment, but it was not statistically significant. All mice, regardless of treatment, receiving doxorubicin showed significant weight loss. It appears that ibuprofen offers little protection against doxorubicin toxicity under these circumstances.