Simple voltammetric determination of thiodiglycolic acid (TDGA) offers the possibility to follow individual deviations in metabolism of thiocompounds and one-carbon (1c) and two-carbon (2c) units, which take part in endogenous synthesis of creatine (CR). In three groups of young men the levels of TDGA in urine were followed after application of CR given as food supplement in 5 g daily doses. In the first group (7 men) it was found that the level of TDGA increased independently of the day time of application of CR. In the second group (9 men) the level of TDGA increased within an interval of 3-8.5 h after CR application and then dropped during 2 h to the normal level (20 mg L-1). In the third group (11 men), in 4 days' study the effects of CR were compared in alternation to vitamin B-12. Vitamin B-12 was given in the evening of the 1st and 3rd day and CR in the morning of the 3rd and 4th day. CR increased the excretion of TDGA in all men, while B-12 only in four men independently of CR application. (C) 2008 Elsevier Ltd. All rights reserved.