The biochemical distribution of ß-glucuronidase activity was studied in different reproductive organs, seminal plasma and spermatozoa of the bull. The highest specific activity was found in the epididymis, where the activity seemed to be mostly in nonsecretory and only partly in secretory form. A molecular weight of 340 X 10^3 to 360 X 10^3 was recorded for ß-glucuronidase in the bull seminal plasma and different reproductive organs with gel filtration on Sepharose 6B. In chromatofocusing four activity areas (CF-1 to CF-4)were usually obtained for ß-glucuronidase in the bull seminal plasma. The major peak CF-2(also in the different reproductive organs) had a pi value of 5.6-5.3 and the two minor activity areas CF-1 and CF-3 had pi values of 6.0-5,8 and 5.2-4.5, respectively. Peak CF-4 eluted with a NaCl gradient after the Polybuffer elution and possibly represents an enzyme form incompletely detached from negatively charged cellular material. Isoelectric focusing on polyacrylamide gel confirmed the heterogeneity of ß-glucuronidase, since several activity bands were detected in the secretion of the different parts of the epididymis. ß-Glucuronidase activities CF-1, CF-2 and CF-3 had similar pFl activity profiles (pH optimum around pH 3.0-4.0) and response to thermal inactivation at 50 °C. The multiple ß-glucuronidase activities of the bull seminal plasma are proposed to derive mainly from the secretion of the cauda epididymidis.