The males of the NICD strain ofAnopheles stephensiwere exposed to 4000 R of Co-60 Gamma radiations at the rate of 188 R per minute and then mated with virgin females of the same age group. The salivary chromosome preparations from 4th instar larvae of F1progeny revealed 40 heterozygous aberrations involving deletions, inversions, translocations and complex rearrangements, however with variable frequencies. The frequencies of breaks per sperm and the mortality induced, thereof, have been determined. It has been concluded that gamma-rays act specifically but not at random. From the available data, it has been deduced that chromosomes had a spiral structure and polar field type of orientation during the irradiation of spermatozoa.