The effects of flavonoids quercetin (Q) and chrysin (Ch) were evaluated in rats with alloxan-induced diabetes mellitus. A single dose of 60 mg alloxan (A) per kg body weight was injected to rats fasting for at least 16 h. Q or Ch in amounts of 50 and 100 mg/kg body weight were administered orally to the control non-treated and A treated rats (10 rats per group) for 3 days prior and 7 days after A injection. Glycaemia, glycosuria, total antioxidant status (TAS) and activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx) were determined. Both Q and Ch prevented serum glucose elevation due to A, but the effect of Ch was weaker, particularly at the higher dose. The beneficial effects of flavonoids on glycosuria and antioxidant status differed between Q and Ch, being generally greater in case of Q, and depended on the dose. It is suggested that the protective effect of flavonoids under study is partly related to their antioxidative/chelatory properties and partly to the alteration of renal glucose absorption.