The amounts ofN‐nitrosoproline (NPRO) excreted in the urine of lacto‐vegetarians and subjects eating a free‐choice diet were determined. The study was carried out during four consecutive weeks and specified extra amounts of ascorbic acid were ingested daily during three of them. The average amount of NPRO excreted in the urine of the lacto‐vegetarians (1.33μg/24h) was slighly smaller than that in the urine of the individuals eating a free‐choice diet (2.13 μg/24 h). Intake of as little as 3 x 20 mg of extra ascorbic acid per day reduced the NPRO excretion. Intake of 3 x 1000 mg of ascorbic acid resulted in a statistically significant decrease in NPRO excretion in the urine.