The storage proteins of Lepidoptera include a pair of methionine-rich hexamerins (MtH) that are more abundant in female pupae than in males. Their inferred support of female reproduction could be achieved either by enhancing general pools of amino acids, or by hydrolyzing MtH at times and/or sites that direct its constituents to the synthesis of egg proteins. The two models were tested in Actias luna, a saturniid moth that makes its eggs during adult development. MtH and arylphorin (ArH), the third major storage protein of this species, were labeled metabolically with [35S]-methionine and [3H]-leucine, and injected individually into wandering stage caterpillars. Isotope distributions at eclosion indicated that both hexamerins supported egg formation as well as adult tissue protein synthesis. In the absence of evidence for targeting, MtH appears to support egg formation in A. luna by enhancing the amino acid pools derived from ArH. Analysis of 35S labeling and of 35S/3H ratios indicated, however, that ArH is consumed over a period that extends somewhat later in adult development than MtH. Differences in timing should prove to be much greater in Lepidoptera that delay egg formation until after eclosion.