Current values for the gut absorption factor of plutonium- 210 ([sup 210]Po) are based on very few human data, yet the dose due to [sup 210]Po is an important component of the dose to man through food as a result of natural sources of radiation. In this study, three male and three female adult volunteers ate supplies of brown crab meat containing natural concentrations of [sup 210]Po, which are analysed from sub-samples. Daily urine and faecal samples, taken for 3 days before and up to 3 weeks after ingestion, were also analysed. Values of apparent absorption were derived from the faecal measurements; estimates of the true absorption were derived taking account of endogenous faecal excretion on the basis of existing data for intravenous administration. The results appear to suggest that the gut absorption factor in current use for [sup 210]Po (in connection with ingestion in food) should be increased from 0.1-03 to about 0.8. The implications for estimates of dose due to this exposure pathway are noted. (author).