Condensational growth of a polydisperse aerosol was studied employing the moment method of log-normal size distribution function. The previous analytical solution for the size distribution of a condensationally growing aerosol (Park et al., J. Aerosol. Sci. 32 (2001) 187) was extended to cover the low Knudsen number transition regime. In order to cover the transition regime, the harmonic mean method was used for obtaining the transition correction factors for mass and heat fluxes. Comparisons were made with the existing solution and good agreement was obtained. (C) 2002 Elsevier Science Ltd. All rights reserved.