When 3-methylhistidine (3MH) excretion is used as an indicator of myofibrillar protein catabolism, there are restricting factors, such as meat intake, incorrect 24-h urine collections, and a large interindividual variation in basal excretion. 1-Methylhistidine (1MH) was previously suggested as an indicator of meat intake. We studied the basal urinary excretion of 1MH and whether this was influenced by infection and we compared the use of 3MH vs the 3MH:creatinine ratio (3MH:Cr) in detecting changes during infection. The basal excretion of 1MH was 84.9 mumol/24 h and its creatinine molar ratio (1MH:Cr) was 7.4 x 10(-3) with no change during infection. Because 1MH:Cr was significantly increased in 4 of 14 patients, their 3MH values were considered influenced by meat intake and thus discarded. Among the remaining 10 patients, 9 showed a significant individual increase in 3MH:Cr during infection compared with only 4 in 3MH. This was due to a higher precision in 3MH:Cr despite the concomitant significant increase in urinary creatinine excretion.