This study was undertaken in order to evaluate differences in pH, cytotoxicity, and concentration of glucose degradation products between different peritoneal dialysis (PD) fluids. Four brands of commercial PD fluids were selected: Gambrosol, Bieffe, Dianeal, and Lock-olys, with a glucose concentration between 3.86% and 4.25%. The cytotoxicity of unused PD fluid was measured as inhibition of cell growth after three days' exposure of a fibroblast cell line using neutral red vital stain. The concentration of 2-furaldehyde, 5-hydroxymethyl-furaldehyde (5-HMF), acetaldehyde, formaldehyde, glyoxal, and methylglyoxal was analyzed by high-performance liquid chromatography technique. All the investigated PD fluids were cytotoxic and contained noticeable amounts of aldehydes. No major differences were observed in pH, although one fluid with a slightly lower pH was found to be less cytotoxic. This fluid also contained less formaldehyde, acetaldehyde, methylglyoxal, and glyoxal but instead contained more 5-HMF. We conclude that all brands of PD fluid are cytotoxic due to glucose degradation products and that they contain noticeable concentrations of low-molecular aldehydes. Our results also demonstrate that the concentration of 5-HMF, used as a regulatory control of PD fluids, does not correlate well with cytotoxicity.