The pharmacokinetic profile of 2,4-D is defined in man. Five male human volunteers ingested a single dose of 5 mg/kg 2,4-D without detectable clinical effects. Concentration of 2,4-D were determined in plasma in 3 of 5 subjects and in urine in all subjects at intervals after ingestion. The elimination of 2,4-D from plasma in all subjects occurred by an apparent first-order rate process with an average half-life (t1/2) of 11.6 h. All subjects excreted 2,4-D in the urine with an average t1/2 of 17.7 h. Excretion occurred mainly as 2,4-D (82.3%) with smaller amounts excreted as a 2,4-D conjugate (12.8%). Essentially all of the 2,4-D was absorbed from the gastrointestinal tract in man. Clearance of 2,4-D from the plasma and excretion from the body are first-order rate processes. There was no evidence that 2,4-D would accumulate following repeated administration.