The noise associated with generation and recombination of carriers in p-n junction transition regions was first considered in detail by Lauritzen and by K. M. van Vliet. Their theory is used to explain the g-r noise in the recombination current. They pointed that the noise from generation-recombination centers appears not to be particularly significant in BJTs. However, in this study, we have demonstrated that the g-r noise, caused by generation and recombination of carriers in a p-n junction, exists in both recombination current and diffusion current. By noise measurement and theoretical analysis, in the forward-biased junction we find that the g-r noise in the diffusion current may be much greater than the g-r noise in the recombination current. This is particularly significant for evaluating defects in p-n junctions and for reliability screening of BJTs. However, in the low-biased or reverse-biased junction the g-r noise in the recombination current becomes dominate. Consequently, the Lauritzen and K. M. van Vliet theory is satisfactory.