Insulin stimulates a profound shift in GLUT4 trafficking to the PM. We have recently developed a GLUT4 construct (rGLUTpHluor), that alongside a specialised workflow allows quantitative stepwise analysis of GLUT4 trafficking and provides a powerful tool for pinpointing regulatory nodes that contribute to insulin regulation and insulin resistance. We have used this methodology to investigate the involvement of the b isoform of Double C2 domain protein (Doc2B) in insulin-stimulated GLUT4 trafficking. Doc2b has been implicated in the fusion of GLUT4 vesicles with the PM. Based on its domain structure Doc2B is thought to promote membrane fusion by inducing positive membrane curvature in a calcium dependant manner (in a manner analogous to synaptotagmins in other cell types). In our hands, Doc2B null mice were mildly glucose intolerant when challenged with a glucose bolus. Insulin-stimulated glucose uptake was compromised in adipose tissue but not muscle of Doc2b KO mice. This suggests that there is an adipose specific defect in these mice that is partially responsible for the observed glucose intolerance. GLUT4 delivery to the PM was impaired in adipocytes isolated from Doc2B KO mice . Detailed analysis of GLUT4 exocytosis suggests this is due to defects at two distinct sites within the GLUT4 trafficking pathway. These data suggest that Doc2b is a key regulator of insulin stimulated GLUT4 exocytosis in adipocytes.