In order to see if NaCl affected the the emergence rate and the SD action when treated it at the pupal stage of Drosophila melanogaster, an experiment was performed in which the resistibility to NaCl at the pupal stage was examined by the emergence rate and the effects of NaCl on the SD action was studied by k values. The four SD strains and two other strains (cn bw and Oregon-R) were used and NaCl media were prepared by adding NaCl at a concentration of 0.0M, 0.1M, 0.3M, 0.5M, 0.7M, and 1.0M to the standard media for the present experiment. The following conclusions were established: 1. The emergence rate (resistibility to NaCl) when treated NaCl at the pupal stage is significantly different not only among the strains but also among concentrations of NaCl. 2. The emergence rate decreases as concentration of NaCl increases but the rate of decrease shows rather constant so that the curves of decrease are not steep. 3. The emergence rate of the cn bw and Oregon-R strains shows higher value than of the four SD strains, implying that the resistibility to the NaCl is lower in the SD strains than in the two strains; not a few flies are emerged from the media of 1.0M of NaCl. 4. The difference in k values is not significant among concentrations of NaCl but among strains, the k values of the original SD strains are rather higher and constant but those of the recombinant SD strains are rather low and unstable. 5. The SD action is not affected by NaCl as far as once emerged from the culture media whether containing NaCl or not in any developmental stage. Thus such an experiment on NaCl effect is of little value to analyze the mechanism of the SD action in D. melanogaster.