This study was carried out to clarify the interaction of oocyte development, protein and hormonal control during the first reproductive cycle in the blowfly, Lucilia illustris. After emergence, all flies were maintained on a diet of sugar and water for the first 5 days of their adulthood. By 6 day, fresh beef liver was provided and samples were collected if necessary. Maturity of oocyte development was examined every 12 hr after liver-feeding and length of primary oocyte showed 1.33 and 1.36 mm at 84 and 96 hr as fully matured. Based on the maturity of oocyte development, changes of protein in fat body, haemolymph and ovary were measured quantitatively and qualitatively. Fat body and haemolymph proteins increased rapidly between 48 and 60 hr while ovarian protein increased from 60 hr to oviposition time. Molecular weight of vitellin purified by TEAE-cellulose column chromatography was 47,000 dalton. Allatectomy and sham-operation were performed as described in Materials and Methods. Allatectomized flies (CA-removed) recovered about 55%. The survived flies significantly retarded oocyte development. It is suggested that the presence of corpus allatum in female fly is essential for normal egg development which begins just after liver-feeding.