Ten patients with type I diabetes were transplanted with porcine fetal islet-like cell clusters (ICC) between 1990 and 1993. A significant rise in the anti-α-Gal antibody titers was seen posttransplant, but also non-α-Gal-specific antibodies were detected in some patients. We have reanalyzed the carbohydrate specificity of antibodies in the sera from seven of these patients taken before transplantation, 1, 6 and 12 months posttransplantation using a glycan array with 200 structurally defined glycans. The main findings were: (i) prepig ICC transplantation patients had antibodies reactive with terminal α-GalNAc (e.g. the Forssman antigen, but not the blood group A determinant in blood group A patients), α-Gal (except blood group B determinants in B individuals), β3-linked Gal especially Galβ1,3GlcNAc even if terminally sulfated or sialylated, β-GlcNAc except if β1,3-linked and oligomannosyl compounds; (ii) the titers of all carbohydrate-specific antibodies detected before transplantation rose after transplantation; (iii) the kinetics of the antibody responses differed between patients; (iv) in some patients antibodies reacting with Galα1,3Lex and several structures terminated with Neu5Gc appeared after transplantation. In conclusion, anti-α-Gal antibodies are the predominant anticarbohydrate antibodies detected after porcine ICC transplantation, with some patients also developing Neu5Gc-specific antibodies. Their clinical significance needs to be established.