The excretion of 65Zn was compared by metabolic balance studies in adult male rats fed purified diets containing 0.8 mmol Zn/kg diet, with and without 40 mmol picolinic acid per kilogram diet, after single intragastric (i.g.) and intraperitoneal (i.p.) doses of the isotope. In a third experiment picolinic acid was introduced for 3 d into the diet of rats prelabeled with 65Zn. The urinary excretion of total zinc was increased by the ingestion of picolinic acid in all three experiments. The urinary and fecal outputs of 65Zn were both consistently greater in picolinic acid-fed rats than in the corresponding control animals. This was particularly marked after i.p. injection of the tracer, and the specific activities of urine and feces from the treated rats were both increased. When picolinic acid was introduced into the diet of prelabeled rats there was a delay of 24 h in the urinary response and 48 h in the fecal response. The residual 65Zn levels were reduced in several tissues from the picolinic acid-fed rats, especially after i.p. administration of the isotope. These observations indicate that dietary picolinic acid increases the turnover of endogenous zinc in addition to enhancing the absorption and excretion of ingested metal, and this has implications for its use in cases of zinc deficiency.