Proteins in homogenates of yolk-rich cricket eggs were fractionated by sonication, differential centrifugation, acetic acid-extraction and column chromatography on hydroxyapatite and separated by SDS-polyacrylamide electrophoresis in 8 M urea. Radioactivity was introduced by incubating the eggs, which are impermeable to labeled amino acids, in a14CO2-atmosphere.14C-label in protein extracts was resistant to hot TCA-extraction and was proved to be mainly in glutamic acid and aspartic acid. The profiles of radioactivity across the electropherogram as analysed by gel-fractionation and scintillation counting or by radioautography were found to be distinct from the pattern of stained protein-bands. During early development characteristic changes in the patterns of radioactive proteins occurred at the three stages tested: cleavage (omnipotency), germ-disc (determination) and germ-band (primary differentiation).