We investigated the reproducibility of the inter- and intra-individual variations in the conversion of nitrate to nitrite in saliva. Saliva samples were collected from 20 volunteers just before and at regular intervals after a nitrate load on four non-consecutive days within a period of 2 months. On three occasions beetroot juice was the nitrate source and on one occasion a nitrate solution was given. Despite large day-to-day variations it was possible to discriminate between subjects with a consistently high or low nitrate conversion after a nitrate load. Neither saliva sampling before a nitrate load nor single saliva samples are sufficient to obtain clear information about individual capacities for nitrate-nitrite conversion.