The recent availability of human insulin raised the question of evaluating its effectiveness in comparison with traditional animal insulins in the treatment of type I diabetics. 9 long-term CSII treated type I diabetics were shifted from pork insulin to human semisynthetic insulin and followed up to 8 months. The following parameters were evaluated: basal insulin infusion allowing morning blood glucose of 100-140 mg/dl and the serum insulin binding capacity (Bio-Merieux). 5 subjects did not show any variation of basal insulin requirement whereas in 4 subjects the occurrence of hypoglycemia induced a reduction of basal insulin requirement of 15%, 16%, 27% and 15%, after 1,2,2 and 8 months respectively, from the shift to human insulin. Serum insulin binding capacity was undetectable in 3 subjects, unchanged in 4, slightly decreasing in 2. One of these two exhibited as well a decrease of basal insulin requirement (16%), while in the other the state of pregnancy prevented its precise assessment. In conclusion human insulin appears as effective as pork insulin; further studies are needed to confirm the suggestions of its lower immunogenicity.