Ejaculation, prostatic massage, prostatic aspiration biopsy, and prostatic punch biopsy were performed in adult male dogs. The dogs had no abnormalities, as determined by physical examination, CBC, urinalysis, and urine culture. In 7 of 18 dogs, results of bacterial culture of an ejaculate were negative. Bacteria of several species, but primarily gram-positive cocci, were isolated from ejaculates from the remaining 11 dogs. The concentration of bacteria varied from 550/ml to greater than 100,000/ml (1 dog). More than one genus of bacteria was isolated from 8 of the 11 dogs with positive culture results. These organisms were attributed to urethral or preputial contamination during collection. The large numbers of organisms isolated from a few dogs indicated the results of culture of ejaculates must be interpreted cautiously when trying to determine whether prostatic infection is present. Low numbers of neutrophils and occasional squamous cells were found in 66% and 50% of semen samples, respectively, but their presence did not correlate with positive culture results. Massaging the prostate was not associated with recovery of cells or bacteria from proximal urethral washes. An adequate specimen of prostatic tissue for microscopic examination was obtained in 8 of 17 dogs by aspiration and in 8 of 12 dogs by punch biopsy. Bacteria were not isolated from 15 of the 16 samples. Small, focal lesions in the prostate were not detected by aspiration or biopsy. Hematuria of less than 4 days' duration and mild periprostatic hemorrhage were the only complications of aspiration or punch biopsy.