In a prospective study on 81 patients undergoing transrectal needle biopsy of the prostate, the efficacy of prophylaxis in preventing postbiopsy infectious complications was determined. The patients were divided randomly into four groups, and a comparison of the rate of postbiopsy complications in each group was made. In 11 and 17% of the patients in Group A (n = 18) who received povidone-iodine enema alone, bacteriuria and bacteraemia, respectively, occurred. When parenteral piperacillin alone in Group B (n = 22) was administered, the rates of the same complications were 9 and 14%, respectively, while both rates were as low as 4% in Group C (n = 25) when piperacillin in combination with povidone-iodine enema was given. On the other hand, in 31 and 37.5% of the patients in Group D (n = 16), who served as controls, bacteriuria and bacteraemia developed. The study has thus shown that parenteral piperacillin in combination with povidone-iodine enema significantly reduces the incidence of infectious complications associated with transrectal prostatic biopsy.