The prostate gland of 11 normal dogs and five dogs with histologically confirmed chronic lymphocytic or lymphoplasmocytic prostatitis were imaged with grey-scale and Doppler ultrasound. Three vessel types (prostatic artery, capsular artery and parenchymal artery) were identified with color Doppler and the resistive index and maximum and minimum velocities were measured with pulsed wave Doppler. No differences between normal dogs and dogs with prostatitis was identified in either grey-scale ultrasound or in any Doppler parameters measured. Regardless of histologic diagnosis, acepromazine (0.05 mg/kg i.v.) caused a significant decrease in capsular artery maximum and minimum velocities and prostatic artery resistive index. This study establishes normal Doppler ultrasound parameters for the intact male canine prostate gland. Additional studies are necessary to further evaluate the clinical utility of Doppler ultrasound in canine prostatic diseases.