The titre of insulin-like-peptides (ILP) in the haemolymph, developing oocytes and developing eggs was examined by a radioimmunoassay for human anti-insulin. ILP in the haemolymph increased in a two-stage pattern during oogenesis, but fell at ovulation. ILP accumulated in the oocyte during the same period but was not detectable in the ovulated oocyte. During embryogenesis three peaks of ILP concentration could be detected in extracts of embryonated eggs. The timing of these peaks was closely correlated with the timing of peaks of ecdysone titre previously reported by Lagueux et al. (1979). It is postulated that the ILP stimulate the previously observed synthesis and release of ecdysteroids during oogenesis and embryogenesis (Lagueux et al., 1979; Porcheron et al., 1982).