Peritoneal dialysis (PD) solutions and therapeutic drugs frequently added to PD solutions in clinical practice have been shown to reduce the viability and to impair the function of mouse peritoneal cells. The cytotoxicity of PD solutions, directly related to the dextrose concentration, was more marked towards resident than elicited peritoneal cells. None of the drug additives, heparin and insulin amongst them, were cytotoxic when tested alone or combined with 4.25% PD solution, with the exception of phosphatidylcholine which markedly enhanced the cytotoxicity of the PD solution. While the function of mouse peritoneal macrophages as measured by their hydrogen peroxide production was largely unaffected by PD solutions and drug additives when tested separately, the combination of 4.25% PD solution with any of the drug additives resulted in complete abolition of macrophage respiratory burst. The results should caution against the indiscriminate addition of drugs to PD solutions in dialysis patients.