The Edmonton protocol for islet transplantation utilizes fresh islet grafts but other protocols increasingly transplant short-term cultured grafts mainly for practical reasons. To improve our understanding of the impact of culture pretreatment of human islets, we assessed post-transplant function by nude mouse bioassay, islet ATP, activity of stress-activated MAP kinases, and expression of stress-related genes by focused cDNA array in freshly isolated and cultured islets. Mean blood glucose levels over 4 weeks after transplantation (2000 IE) of (i) freshly isolated, (ii) cultured and preculture counted (recovery rate; 78 ± 6%), and (iii) cultured and postculture counted islets in diabetic mice were 330 ± 40, 277 ± 65, and 256 ± 52 mg/dl (i versus ii, P = 0.004; i versus iii, P = 0.002). During culture, islet ATP/DNA and ATP/ADP increased; JNK and p38 MAPK activities decreased. Among 96 genes studied, mRNA expression of heat shock protein 70 genes decreased >twofold during culture in all four pairs; expression of cyclooxygenase-2, superoxide dismutase-2, interleukin-6 and cytochromes P450 1A1 genes increased. Our results show that culturing human islets before transplantation is not disadvantageous in regard of functional recovery from changes induced by nonphysiologic stimuli during islet isolation. The increase in expression of several stress-related genes during culture also shows that improving culture conditions may further enhance post-transplant islet function.