Abstract: Pharmacokinetics of phenithionate (phenyl 4-nitrodiphenylamino-4′-thioncarbamate), a new compound related to Amoscanate, was studied by quantitative TLC scanning technique which was specific and sensitive for detection of phenithionate in plasma, and by which its plasma metabolite, Amoscanate, Could be determined simultaneously. The lower limit of detection of phenithionato amounted to 0.1 μg. The coefficient of variation was less than 10%. The average recovery was 80%.Phenithionate achieved the highest concentration, reaching peak value of 0.51 μg. ml^-1 in rat plasma at 6 h after ig administration of the drug by a single dose of 200 mg/kg. A two-compartment model for phenithionate described the plasma concentration-time curve, The pharmacokinetic parameters were as follows: t1/2ka 1.5 h; t1/2α, 2.8 h; t1/2β, 17.769 h; K₁₀, 0.068 h^-1; K₂₁, 0.141 h^-1: K₁₂, 0.075 h^-1; AUC, 12.367 μg.h.ml^-1. It was shown that phenithionate was stable in gastrointestinal tract but its metabolite Amoscanate, appeared in the rat plasma within 1 h and reached the peak level at 6 h after administration of phenithionate with a peak value of 0.283 μg.ml^-1 in rat plasma. AUC from O to 36 h of phenithionate and Amoscanate calculated by trapezoidal rule was 9.211 and 4.644 μg.h. ml^-1, respectively. AUC of phenithionate was twice that of Amoscanate.