The interactions between genetic and environmental factors on the development of lamb affinity to humans was assessed on 48 animals from two breeds (Gentile di Puglia and Comisana) and two treatments (Gentled and Not Gentled) producing 4 groups (GPg, GPng, Cg, Cng, respectively). The Gentile di Puglia and Comisana gentled animals were subjected to a period of training consisting of gently handling each lamb for 5 min three times a day for the first week and then twice a week for three additional weeks. The gentling procedure included both tactile and visual/auditory interactions. At 30-32 days of age lambs were subjected to three arena tests conducted in a novel environment: i) isolation test (each animal was exposed to a novel environment, and isolated from tactile and visual contact with conspecifics for 5 min), ii) stationary human test (as previously but a human sitting in a corner of the pen), and iii) pen-mates' test (each animal was tested in the presence of 2 pen-mates whose behaviour was not recorded). During the 13 training sessions lambs exhibited an increasing number of contacts with the human and a decreasing number of bleats (P<0.001), although Gentile di Puglia lambs interacted more with the human (P<0.001) and tended to bleat less (P<0.10) than Comisana lambs. Lambs vocalised more and climbed more when tested in isolation as compared with lambs tested either with the human or with the pen-mates (P<0.01 ) and they vocalised more in the presence of the human than with the pen-mates (P<0.001). A higher number of contacts with the human stimulus was observed in gentled animals (P<0.05). However, differences between gentled and not gentled animals were only significant in Gentile di Puglia subjects (P<0.01). GPng lambs displayed the longest ambulatory activity during the isolation test (P<0.05) and exhibited more climbing attempts during the isolation test as compared with the human or the pen-mates' tests (P<0.001). A higher cortisol level was shown by GPng lambs in comparison with Cng subjects during the stationary human test (P<0.01), whereas no differences were detected between the two gentled groups. Gentling determined an improvement of the quality of human animal relationship in more reactive breeds such as Gentile di Puglia sheep.