No differences were noted in the amount of naphthalene uptake (approximately 125 :g) by individual crayfish exposed for 1, 2, or 4 hr at 25?C in open, non-aerated glass jars containing14C-naphthalene-5% of a water-soluble fraction (WSF) of No. 2 fuel oil. The cephalothorax, containing the hepatopancreas (a food absorption organ), showed greater uptake of naphthalene than the tail flesh or tail skeleton of individual crayfish exposed to the oil for 3 hr at 25?C. Crayfish exposed to the oil for 1, 2, or 4 hr and then placed in open, non-aerated containers of oil-free water lost most of the carbon-14 activity during the first 24 hr, with smaller losses occurring at 24 hr intervals up to and including 96 hr. Carbon-14 naphthalene in a 5% WSF of No. 2 fuel oil held in 12 open, non-aerated, oil-free, glass jars for 1, 2, 3, 4, and 5 hr at 25?C showed little volatilization (P > 0.4).