The detailed electronic structures of several materials of organic solids, ((Formula presented),(Formula presented)-DCNQI(Formula presented)M, were studied with the first-principles method based on the local-density approximation supplemented by the generalized gradient approximation. The present calculations account well for the qualitative differences in the electronic properties produced by different metal cations (M=Li, Ag, and Cu). Unique aspects of the systems with (Formula presented)=(Formula presented)=I are also explained based on the present calculations. The very small hole Fermi surface observed by the de Haas-van Alphen measurement for (DMe-DCNQI(Formula presented)Cu was well reproduced by the calculation with the observed crystal structure. © 1996 The American Physical Society.