In this study the expression of uncoupling protein 3 (UCP3) and its regulation by insulin-like growth factor 1 (IGF-I) and insulin in human neuroblastoma SH-SY5Y cells were characterized. Reverse transcriptase-PCR, Western blot, and immunofluorescence analysis showed that SH-SY5Y cells express UCP3 natively. IGF-I induced a time- and concentration-dependent induction of UCP3 protein reaching a twofold expression after 72 h with 10 nM IGF-I. Extremely high insulin concentrations (860 nM) and 10 nM trIGF-I, a truncated form of IGF-I with the same affinity for the IGF-I receptor as the full-length IGF-I, but with lower activity on the insulin receptor, also upregulated UCP3. We conclude that SH-SY5Y cells express UCP3 natively and that the expression is regulated by IGF-I via the IGF-I receptor.