Chloroquine, the commonly used in the treatment of malaria has been reported to elicit adverse effects such as hypoglycaemia through unknown mechanisms. In particular, literature to date has revealed that the effects of the drug on insulin concentrations remain obscure. Our investigation therefore focuses on establishing a possible mechanism of CHQ-induced hypoglycaemia with regards to its effects on plasma insulin concentrations. The purpose of this study was to investigate to investigate the effects of chloroquine on blood glucose and insulin concentrations in male SpragueDawley rats. Oral glucose tolerance (OGT) responses were conducted in separate groups of rats given glucose load (0.86 g/kg, p.o.) after 18 h fast, followed by various CHQ doses (30, 60, 120 mg/kg, p.o.). Rats treated with deionized water (3 ml/kg, p.o.) served as control animals. Blood glucose was monitored at 15 min intervals for the first hour, and hourly thereafter for 3 h. Plasma insulin concentrations were measured in separate groups of rats treated with chloroquine (60 mg/kg, p.o.) after 0 h (control) and 4 h. Plasma obtained was analysed for chloroquine and insulin concentrations. Blood glucose concentrations in untreated rats significantly (P<0.05) increased from a fasting level of 3.66±0.146.50±0.20 mmol/l 15 min after a glucose challenge. The mean blood glucose concentration declined by the end of the experiment to reach levels that did not significantly differ from the initial concentration. The blood glucose lowering effects of all doses of CHQ were pronounced in the first hour following the glucose load. All doses of CHQ showed blood glucose lowering effects which did not exhibit dose-dependency. Chloroquine additionally increased in plasma insulin concentrations. Since CHQ reduced blood glucose concentration with concomitant increase in plasma insulin concentration, we suggest that the reported hypoglycaemic effect of the anti-malarial is mediated via increased pancreatic insulin secretion.