Post-transurethral resection (TUR) status in the prostate and urinary bladder has been infrequently documented. Furthermore, sequential changes in eosinophil count in peripheral blood (PB) after TUR have not been investigated in detail. In the present study, eosinophil counts and changes in eosinophils in PB were examined before to after TUR of the prostate (P) in 20 patients with benign prostatic hyperplasia. Among them, 14 patients exhibited increased numbers of eosinophils, the greatest increase being 17%. After TUR to treat bladder tumor (BT), massive infiltration of eosinophils into the resected areas, peaking 1 month later, was also detected in 8 of 15 cases of post-TUR cystitis. The PB eosinophil counts increased by more than 5% in two of five cases of post-TUR cystitis in which eosinophil counts were obtained before and after surgery. Most infiltrating eosinophils reacted positively to antibodies to eosinophil cationic proteins. These results indicated that, in patients with post-TUR prostatitis, the number of eosinophils in PB increased, and peaked 1 month later, with infiltration by eosinophils observed. Pathologists and urologists should be aware of the potential for increase in eosinophils not only in regions of TUR but also in PB.