Male rats were used to study the inorganic (ionic) and organic fluoride concentrations in plasma, liver, kidneys and stomach content after oral doses of 0, 2.2, 3.5, 4.0, 5.0 and 7.0 mg sodium monofluoroacetate (SMFA, Compound 1080)/kg body weight. Tissue and plasma ionic fluoride concentrations were observed to be higher in all rats given SMFA as compared to rats in the control group. This observation suggests in vivo defluorination of SMFA. Homogenates of liver obtained from SMFA poisoned rats showed significant increases in ionic fluoride concentration during a 6-day storage period at +4 degrees C, with the total fluoride concentration (ionic and organic) remaining constant. The average percentages of distribution of SMFA (organic fluoride) in plasma, liver, and kidneys were 7.05, 5.07 and 1.68, respectively. Plasma and tissue SMFA concentrations were generally lower than the corresponding stomach fluid SMFA concentrations for all dosage groups. Lethal concentration of SMFA in the liquid stomach content was in the range 84.9--189 micrograms/ml, corresponding to total (ionic and organic) fluoride concentrations in the range of 16.1--36 micrograms/ml.