Impaired insulin secretion is a cardinal defect that results in the hyperglycaemia present in diabetes. We have previously shown that regulating the expression of the endoplasmic reticulum gene Herpud1 can affect insulin secretion. To explore this further we have obtained whole-body Herpud1 knockout mice (Herp-ko) and assessed glucose tolerance, insulin sensitivity and insulin secretion in vitro following high fat feeding for 8 weeks.  At baseline (8 weeks of age) there were no difference in body weights (25.0±1.0 vs 26.0±0.9 g) 6-hour fasted glucose (11.3±0.7 vs 10.0±0.7 mM) or insulin (1.2±0.2 vs 1.1±0.3 ng/ml) concentrations between Herp-ko and littermate control mice.  Eight weeks on a chow diet did not reveal a difference in body weight, 6-hour fasted plasma glucose or insulin concentrations or glucose tolerance between Herp-ko and control mice (data not shown). However following 8 weeks of high fat feedin g Herp-ko mice displayed glucose intolerance (AUCglucose: 1791±55.1 vs 1552.0±59.1 mMx120 min P<0.01) despite no difference in body weight (30.7±0.7 vs 31.2±1.5 g), plasma insulin levels during the glucose tolerance test (AUCinsulin: 356.1±22.9 vs 302.0±37.6 ng/mlx120 min) or insulin sensitivity (AUCglucose: 483.8±12.8 vs 491.6±28.5 mMx60min).  Interestingly when islet insulin secretion was assessed in vitro following high fat feeding there was no difference in basal (2.8 mM: 0.034±0.015 vs 0.033±0.011 ng/islet/60min) but there was a significant reduction in glucose stimulated insulin (20 mM: 0.395±0.038 vs 0.501±0.034 ng/islet/60min, P<0.05) in Herp-ko vs control mice. In conclusion the absence of Herpud1 leads to fat-induced glucose intolerance associated with impaired glucose-mediated insulin secretion, supporting a significant role for this gene in glucose homeostasis.