Little is known of the influence of nutritional status on cytochrome P450 (CYP) 1A2 activity in elderly patients. Thirty elderly institutionalised patients with malnutrition (group A, aged 88 +/- 5 years) and 24 without (group B, aged 81 +/- 9 years) were included. Malnutrition was defined as weight loss of >10% over the previous 6 months and/or a body mass index (BMI) <21 kg/m2 and albuminaemia < or = 32 g/L. CYP1A2 activity was evaluated by the plasma paraxanthine/caffeine (PAX/CAF) metabolic ratio. The plasma PAX/CAF metabolic ratio was similar in both groups regardless of nutritional status (0.34 +/- 0.13 [A] versus 0.30 +/- 0.11 [B]; p = 0.11). The CYP1A2 metabolic ratio was not correlated to either BMI, serum albumin or renal clearance. CYPI A2 activity, as measured by the plasma PAX/CAF ratio, was not influenced by nutritional status in elderly patients.