1. A method for measuring vinyl chloride monomer (VCM) concn. in rat blood and tissues is described, using a head-space g.l.c. technique with flame ionization detector. The method is sensitive to 5 ng/ml VCM in blood and 30 ng/g in tissues. 2. VCM disposition was determined in rat blood, liver, kidney, brain and lung at different intervals after administration of 1--10 mg VCM/kg i.v. and 10 mg/kg orally. 3. VCM distributed rapidly in the organism after i.v. administration; it was eliminated rapidly and was no longer detectable at 15 min for the highest dose and at 4 min for the lowest. VCM was absorbed rapidly when given orally and tissue concn. were measurable for longer than after i.v. treatment. For both routes, VCM concn. in liver and lung decrease faster than in other organs, suggesting that these organs play a role in VCM elimination.