The ref(2)P gene is a Drosophila gene which acts on Sigma virus multiplication. From recombination experiments the ref(2)P gene was located between hk and pr. This location was confirmed by the study of eight chromosomic aberrations, without ref(2)P gene activity, obtained following X irradiation. From the cytological study of three of these chromosomes and from the study of the ref(2)P gene activity of chromosomic aberrations obtained by other workers in the same region of the second chromosome, the ref(2)P gene was cytologically located in 37E3-37F3.