Male largid bugs,Physopelta schlanbuschi, having 2n=17 chromosomes (12 autosomes +2m+X1X2Y), were irradiated with x-ray doees of 300 r, 400 r and 500 r which yielded various types of chromosome aberrations in different stages of meiosis of which the common forms were breaks, fragment of unknown origin, constriction, gap etc. Among the 3 sex chromosomes, the two conspicuously large markers, X1 and Y, sometimes formed chiasmalike configuration in prophase I and metaphase I, while a number of anaphase I plates had a chromatid bridge, very likely formed by the X1 and the Y. The qualitative and quantitative assessments of chromosome aberrations in spermatogonial metaphase, prophase I, metaphase I, anaphase I and metaphase II were made at 13 intervals for the doses of 300 r and 400 r and 14 intervals for 500 r between 5 min and 1 week or more. The data showed over-all dose-dependent aberration effects and the sex chromosomes appeared relatively more vulnerable than the autosomes to different doses of x-rays. The testes of untreated males taken as controls had practically no aberration.