Human metabolism of di(2-ethylhexyl)phthalate (DEHP) was studied after a single oral dose of 48.1mg to a male volunteer. To avoid interference by background exposure the D4-ring-labelled DEHP analogue was dosed. Excretion of three metabolites, mono(2-ethyl-5-hydroxyhexyl)phthalate (5OH-MEHP), mono(2-ethyl-5-oxohexyl)phthalate (5oxo-MEHP) and mono(2-ethylhexyl)phthalate (MEHP), was monitored for 44h in urine and for 8h in serum. Peak concentrations of all metabolites were found in serum after 2h and in urine after 2h (MEHP) and after 4h (5OH-MEHP and 5oxo-MEHP). While the major metabolite in serum was MEHP, the major metabolite in urine was 5OH-MEHP, followed by 5oxo-MEHP and MEHP. Excretion in urine followed a multi-phase elimination model. After an absorption and distribution phase of 4 to 8h, half-life times of excretion in the first elimination phase were approximately 2h with slightly higher half-life times for 5OH- and 5oxo-MEHP. Half-life times in the second phasebeginning 14 to 18h post dosewere 5h for MEHP and 10h for 5OH-MEHP and 5oxo-MEHP. In the time window 36 to 44h, no decrease in excreted concentrations of 5OH- and 5oxo-MEHP was observed. In the first elimination phase (8 to 14h post dose), mean excretion ratios of MEHP to 5oxo-MEHP and MEHP to 5OH-MEHP were 1 to 1.8 and 1 to 3.1. In the second elimination phase up to 24h post dose mean excretion ratios of MEHP to 5oxo-MEHP to 5OH-MEHP were 1 to 5.0 to 9.3. The excretion ratio of 5OH-MEHP to 5oxo-MEHP remained constant through time at 1.7 in the mean. After 44h, 47% of the DEHP dose was excreted in urine, comprising MEHP (7.3%), 5OH-MEHP (24.7%) and 5oxo-MEHP (14.9%).