The present study was undertaken to estimate bio-availability and biological half-life of fluoride and accumulation of fluoride in bone in the domestic pig. Eight animals receiving 2 mg F-/kg b.w. per day from age 8 to 14 months were compared with eight controls. Plasma fluoride concentrations just prior to the daily oral dose were measured at regular intervals. After 112 days post-dose, plasma fluoride levels were measured over a 48-hour period following the daily oral dose or a single intravenous dose. Mean bio-availability factor for the oral dose was 0.3 (range 0.2-0.4), and mean biological half-life was 59 days (range 49-72). Bone fluoride content calculated from the pharmacokinetic parameters derived from plasma data was similar to the content of fluoride measured in the bone at slaughter. The study showed that accumulation of fluoride in bone influences plasma fluoride levels during chronic administration of fluoride to growing pigs. The long biological half-life found showed that it was not possible to achieve steady-state plasma levels within the six-month experimental period used. This means that, for dose-response studies of dental fluorosis in this animal, it is not possible to achieve steady-state plasma concentrations as a basis for correlations to the degrees of pathological change observed in the teeth.