Karakul ram lambs were divided into three groups after weaning and treated as follows: Group A: Total isolation; Group B: Contact with ewes until 9 months and then isolated; Group C: Isolated from ewes until 9 months and then allowed contact. At 18 months the rams were penned and then tested in pairs on oestrous ewes to establish a rank order for libido. Subsequently all rams were introduced individually for 10 minutes in a sequence of 5 replications to oestrous ewes in a 3 x 3 m pen. Libido, mating dexterity as well as the time lapse to first copulation and total copulations were recorded. Totally isolated rams reacted poorly and only 44 %compared with 88 and 100%respectively of the rams in Groups B & C showed normal mating behaviour. Rams in Group C experienced a growth surge after introduction of ewes at 9 months of age and the possibilities of sexual contact resulting in greater testosterone and/or growth hormone release, is discussed. It was concluded that the practice of isolation of ram lambs after weaning is detrimental to normal sexual behaviour and that hetero-sexual contact prior or subsequent to puberty could be of practical importance. A simple libido test to eliminate sexually inhibited rams at an early stage is recommended.