1. The dispositions of two acetylcholinesterase reactivators, pyrimidoxime and HI6, labelled with 14C on the oxime group, have been studied in normal rats and rats poisoned by the organophosphates Soman and A4. 2. For both compounds, and for healthy and poisoned rats, radioactivity was eliminated essentially in the urine (85% dose in 24 h). Faecal elimination was low (4% in 72 h). 3. Both compounds were concentrated in kidney and mucopolysaccharide-containing tissues such as cartilage and intervertebral disc. Soman and A4 poisoning do not modify the kinetic parameters of pyrimidoxime, but A4 poisoning increases HI6 tissue concentration. 4. Chromatography of urine and plasma showed only unchanged pyrimidoxime in both healthy and poisoned animals. In contrast, HI6 in plasma and urine was strongly degraded by scission of the quaternary ammonium bond, and formation of 2-pyridine aldoxime.