ABSTRACT:A study was made of 73 elderly patients receiving methenamine and ascorbic acid concurrently. Each patient had an indwelling Foley catheter. Urinary pH was assessed in relation to the dosage of ascorbic acid, duration of therapy, formulation, and dosing intervals for ascorbic acid and methenamine. Statistical analysis revealed a significant increase in urinary pH when the dosage of ascorbic acid was increased. No significant relationships were found between urinary pH and the dosage forms of ascorbic acid, the salt of methenamine used, or the duration of methenamine therapy. Changes in urinary pH at different dosing intervals for ascorbic acid were found to be significant, at the 10 percent level only, for the three‐times‐daily dose schedule. These data raise a question as to the value of ascorbic acid for acidifying the urine of catheterized patients receiving methenamine ther