Rowachol (Rowa Ltd., Bantry, Eire), a proprietary choleretic containing the purified mono- and bicyclic monoterpenes menthol (32% w/v), pinene (17% w/v), menthone (6% w/v), borneol (5% w/v), camphene (5% w/v), and cineole (2% W/V) in olive oil, has been shown to cause dissolution of cholesterol gallstones in man (Doran et al., 1979) and to inhibit hepatic HMG-CoA reductase in rats (Middleton et al., 1979) and man (Ellis et al., 1981) when administered in vivo. The present study was therefore designed to investigate the effect of menthol on water with electrolyte excretion and blood glucose concentration in rats. Menthol was administered in olive oil by gastric tube in a volume of 2ml/kg. In determining the dose-response relation for menthol, it was given at 1.0, 3.0 and 6.0 mmol/kg of body weight in a volume of 2 ml/kg. Water together with electrolyte excretion and blood glucose concentration were investigated using flame photometric and colorimetric techniques in rats (n= 48). Values are means ± S.E.M. and compared by one -way ANOVA using Graph Pad prism 4. The treatment of rats with menthol resulted in a decrease in blood glucose concentration (73.0 ± 1.39, 67.5 ±1.41 and 63.9 ±2.06 mg/dl) that was significant (p< 0.05) in all the menthol treated animals (1.0, 3.0 and 6.0 mmol/kg) compared to that of the olive oil treated control group (75.4 ± 1.10 mg/dl). There was a significant dose (p <0.05) dependent increase in urine Na+ ion level (420 ± 15.00, 450 ± 8.86, 480 ± 10.52 mmol) and urine output volume (150± 5.67, 200± 9.82, 280± 11.02 ml) in menthol treated animals compared to their control groups 400± 12.82 mmol and 135± 6.55 ml respectively, while urinary K+ excretion showed no significant change (p>0.05) in all the treated animal groups (86± 2.08, 87 ± 2.38, 89±2.09mmol) with respect to the control (81.5 ± 1.75 mmol). The data obtained indicates that menthol increases water intake, urine output and urine Na+ excretion, and decreases blood glucose concentration. The ethical guidelines in accordance with NIH Guide for care and use of laboratory animals and with the Organization for Economic Development (OECD) guidelines on good laboratory practice (OECD, 2001) were followed in the handling of the experimental animals during the studies.