During the past decade the attractiveness of various hydrolyzed proteins to several species of tephritid flies has been established and these materials have been used in poison bait sprays, in fly traps, and in studies on dispersal habits. Several workers have reported more satisfactory control when enzymatic yeast hydrolysates or acid hydrolysates of corn protein were added to malathion sprays: Steiner (1952, 1955a, and 1955b) for the Mediterranean fruit fly (Ceratitis capitata Wied.), the oriental fruit fly (Dacus dorsalis Hendel), and the melon fly (Dacus cucurbitae Coq.); Shaw (1955) for the Mexican fruit fly (Anastrepha ludens Loew); Orphanidis et al. (1958) for Dacus adults on olives; and Marucci (1958) for the blueberry maggot (Rhagoletis pomonella (Walsh). Orphanidis et al. have also reported that the addition of casein hydrolysate or the acid hydrolysates of corn protein to the recommended lure of ammonium sulphate increased the captures of Dacus as much as twelve times. Although most of the work with these attractants has concerned control, Barnes (1959) has used them to advantage in biological studies. He labelled natural populations of the walnut husk fly, Rhagoletis completa Cress., with a radioactive tracer by attracting the flies to feeding stations of Staley's insecticide bait No. 7 (acid hydrolysate of corn protein) plus the isotope P32 By subsequent trapping he determined the field movements of the adults in and out of walnut orchards.