Bacterial culture and cytology of semen, bacterial culture and cytology of prostatic fluid washings, urinalysis, bacterial culture of urine, and blood leukocyte counts were performed on specimens from dogs with prostatic hyperplasia, chronic prostatitis, or prostatic neoplasia. Hemorrhage was the most frequent abnormal finding in semen from dogs with prostatic hyperplasia. Inflammation was the most frequent abnormal finding in dogs with chronic prostatitis. Bacterial culture of semen was sensitive but not specific for chronic bacterial prostatitis, due to false-positive results from urethral contamination. Hemorrhage was the most frequent abnormal finding in prostatic fluid washings from dogs with prostatic hyperplasia. Inflammation was the most frequent abnormal finding in dogs with chronic prostatitis. Abnormal epithelial cells were found after prostatic massage in 4 dogs with neoplasia, although these cells were difficult to identify as neoplastic. Prostatic fluid washings were not useful for detecting chronic bacterial prostatitis, due to an inability to detect increases in bacterial counts in the fluid when urine bacterial counts were high. Hematuria was the predominant abnormal finding in urinalysis from dogs with hyperplasia and neoplasia. Pyuria was the most frequent abnormal finding in dogs with chronic prostatitis. Urine was usually culture-positive when there was prostatic infection. Blood leukocyte counts were normal in dogs with prostatic hyperplasia and usually normal in dogs with neoplasia. Leukocytosis, a left shift, and toxic white blood cells were predictive of abscessation, although the blood leukocyte count was not a very sensitive indicator for infection without abscessation.