A major challenge to urologists with respect to bladder cancer is the high rate of tumor recurrence after transurethral resection (TUR). Implantation of resected tumor cells on traumatized bladder urothelium is believed to be the main cause of tumor recurrence. The aim of this study was to find a safe irrigant fluid and modality that prevents reimplantation of malignant cells during TUR. Therefore, the cytotoxicity and antiadherence effects of polyethylene glycol 400 (PEG400) and PEG4000 were investigated and compared with currently used irrigant fluids, water and 1.5% glycine (G-IF), on the RT112 urothelial cell carcinoma cell line. PEG400 (20%), G-IF, water and to a lesser extent 10% PEG400 and PEG4000 showed dramatic cytotoxic effects, besides exhibiting interesting antiadherence characteristics. The presence of serum proteins did not interfere with the activity of PEG400. In a clonogenic assay, both water and 20% PEG400 showed a better cytotoxic profile than G-IF, and it was found that these two fluids were able to induce a 5-log kill. This study shows that a solution of 20% PEG400 in water is a promising irrigant with antiadhesive and cytotoxic properties, which could be used to prevent tumor cell reimplantation during TUR. The irrigant remains active in the presence of serum proteins, is transparent, inexpensive and possesses an excellent safety profile.