Des(1-3)IGF-I, a truncated variant of human IGF-I with the tripeptide Gly-Pro-Glu absent from the N-terminus, has been isolated from bovine colostrum, human brain and porcine uterus. This protein probably results from post-translational cleavage of IGF-I. Des(1-3)IGF-I generally is about 10-fold more potent than IGF-I at stimulating hypertrophy and proliferation of cultured cells, a consequence of much reduced binding to IGF-binding proteins, in turn caused by the absence of the glutamate at position 3. The increased potency is retained in part when the variant is administered in vivo, with selective anabolic effects particularly evident in gut tissues. Clinical opportunities for des(1-3)IGF-I have not yet been evaluated, but could apply in catabolic states as well as for the treatment of inflammatory bowel diseases.