Three hundred and forty-nine second chromosomes were extracted from a Taejeon population of Drosophila melanogaster in Korea. Chromosomal inversions and viabilities for homozygotes and heterozygotes were investigated. The number of inversion-carrying chromosomes was 81, among which 50 carried In(2L)t. The frequency of lethal chromosomes(Q) was 0.226(79/349): 0.259(21/81) for inversion-carrying lines and 0.216(58/268) for inversion-free lines. The difference was mainly due to a linkage disequilibrium between In(2L)ts and some lethal genes. Total homozygous load(T) was 0.414, which was partitioned into 0.255 of lethal load(L) and 0.159 of detrimental load(D). In heterozygous condition, the degree of disadvantage of lethal genes (hl) was estimated to be 0.005 per locus on the average. On the basis of the genetic load and the degree of disadvantage, mutation rates of lethal gene per chromosome per generation(U) was estimated to be 0.0013. In heterozygous condition with Cy balancer chromosome, the mean productivity of lethal chromosomes was 379.0 which was significantly different from 339.4 of non-lethal chromosomes, particularly, in inversion-free chromosome lines. The regression coefficients between the heterozygote viability and the sums of corresponding homozygote viabilities was estimated to be close to zero. Allelic rate among lethal chromosomes (Ic) was 0.021, and clusters of identical lethal genes were observed. The effective population size (Ne) then was estimated to be small or 3,500 paris when standard mutation rates were used (i.g., U=0.005 and u=10-5), but it could be re-estimated to be large or 14,000 pairs when the above estimate was used (i.g., U=0.0013 and u=3×10-6). On the basis of the above findings, the genetic load may be primarily to be heterotic and not classical, so much so that this is the major factor in determining their frequency at least in the present population, partly associating with inversions.