Testicular development from 3 to 14 months of age was examined in Dorper (DD), Dohne Merino (DM) and crossbred (Meatmaster; MM) rams. Testicular measurements included testis volume (TV), diameter (TD), length (TL) and scrotal circumference (SC). Both TD and SC were highly repeatable and positively correlated with live body mass and other testicular measurements. Both SC and TD showed significant breed differences (P <0,05) from 3 to 10 months of age which disappeared later on. Non-linear equations were fitted for testicular measurements on age for each breed group. Testicular growth patterns are more similar in the mutton breed types (DD and MM) and differ from dual-purpose DM. This difference probably indicate earlier puberty in the DD and MM breeds. In an attempt to account for body size differences, a SC : live body mass ratio is recommended as a practical selection criterion. A more rapid decrease in this ratio is indicated in the DD and MM breeds compared to the DM, probably because of later puberty in the latter. Individual ratios within and between breed groups varied from 0,378 to 0,948 cm/kg.