In this paper we use the second virial approximation to study the nematic-isotropic (N-I) transition for a Gay-Berne liquid for a broad range of parameters. For Gay-Berne hard Gaussian overlap (HGO) fluid particles we found that a N-I transition exists as a function of density for all length to breadth ratiosk> 4, in reasonable agreement with other theoretical studies and results of Monte Carlo simulations. For the full Gay-Berne potential (GB) the location of the N-I transition as a function of density for different temperatures was studied for several values of shape and energy anisotropy parameterskandk′. It was shown that the transition temperature increases or the transition density decreases with increasingkand/or decreasingk′. Wherever the molecular dynamics (MD) or Monte Carlo (MC) data were available, comparison was made. For each system, coexistence density and pressure were calculated, and, wherever possible, also compared with MC or MD data to show qualitative agreement. The reported study is considered to be a first step in the calculation of N-I transition for rigid liquid crystal (LC) molecules.