A two-dimensional polyacrylamide gel electrophoresis procedure has been used to study ribonucleoprotein synthesis and accumulation at three stages (Dumont stages 1, 2, and 6) of oogenesis in Xenopus laevis. Ribonucleoprotein particles are separated effectively by sucrose gradient centrifugation of oocyte homogenates. Extraction of protein from different sucrose gradient fractions has enabled identification of four classes of ribonucleoprotein (7 S RNP, 42 S RNP, messenger RNP, and 80 S ribosome RNP). Proteins were extracted from subcellular fractions of defined numbers of defollicled oocytes which had been incubated with [ 35S]methionine for 20 hr previously. Electrophoresis first in a Triton X-100-acid-urea polyacrylamide gel followed by a sodium dodecyl sulphate-gradient gel system adequately resolved most of these ribonucleoproteins. A rough estimate of the relative amount of a particular protein was obtained by visual inspection of Coomassie blue-stained gels. Estimates of the relative rates of synthesis of particular proteins were obtained by visual inspection of fluorographs prepared from the gels. Each of the protein classes identified follows a distinct and different pattern of synthesis and accumulation during oogenesis, and appears to be coordinately regulated with the RNA molecule to which it associates.