1. Following intravenous administration of 3',4',7-tri-O-(beta-hydroxy[14C2]ethyl)rutoside or 7-mono-O-(beta-hydroxy[14C2]ethyl)rutoside to male mice, 68% of the dose of each is excreted in faeces as the corresponding hydroxyethyl-quercetin within 72 h of dosage. Mean urinary excretions of mono- and tri-hydroxyethylrutosides in 72 h were 27 and 21% respectively. Unchanged rutosides and their glucuronides were detected in urine. 2. In biliary-cannulated animals, the mean biliary excretion of both tri- and mono-hydroxyethylrutosides was 71%, in 24 h of dosage. In both cases most 14C was excreted in 3 h, as unchanged rutosides and glucuronide conjugates. 3. Fall of blood 14C concn, was rapid for both compounds. Neither compound was detected in brain but there was short-term accumulation in liver and kidney, and 2--3 h after dosage, most 14C for both compounds was associated with the gastro-intestinal contents. 4. Animals killed 72 h after dosage of either compound contained less than 7% of dose, mostly in the colon and caecal contents. 5. Foetuses removed 3 h after dosage of either compound to the dams did not contain 14C; foetuses removed 5 min after dosage contained low levels of 14C, substantially below the maternal blood level and equiv. to less than 0-1% of dose in each case. No 14C was detected in amniotic fluid.