Although immature albacore tuna, Thunnus alalunga, are of economic and social importance in the Bay of Biscay, little is known about their diet and feeding ecology there. For this study, the diet of 78 albacore caught in the French driftnet fishery during summer 1993 is analysed. Fish dominated the diet in terms of relative abundance (86%N), and reconstituted mass (60%M), the most important being ... [Show full abstract] Maurolicus muelleri (79%N, 23%M), Scomberesox saurus (2%N, 30%M), and Arctozenus risso (4%N, 4%M). Crustaceans were also important in the diet (12%N, 2%M), but given their small size, it is questionable whether they were primary or secondary prey. Foraging on cephalopods seemingly took place only occasionally: they represented 2%N and 39%M of the total diet, but were absent from the fresh fraction of stomach contents. Prey sizes ranged from 6 to 228 mm. Juvenile albacore consume either epipelagic prey by day, or vertically migrating mesopelagic species that reach the surface layer by night.