The predicted capture rate in the Cl37 experiment for detecting solar neutrinos is calculated using the results of recent nuclear experiments and solar-model investigations. It is shown that additional experiments (e.g., with H2, Li7, B11, or ν-e scattering) are necessary to establish the relative contributions of the proton-proton chain and the CNO cycle to solar energy generation. ; ©1966 The American Physical Society. Received 11 July 1966. I am grateful to D. Goosman, R. W. Kavanagh, P. D. Parker, and A. M. Poskanzer for supplying me with vital experimental data prior to publication, and to A. G. W. Cameron, D. Ezer, and R. L. Sears for providing detailed information regarding their solar models. It is a pleasure to acknowledge informative conversations with R. Davis, Jr., W. A. Fowler, J. Faulkner, and I. Iben, Jr.