The cytogenetic region 46C-F on the right arm of Drosophila chromosome 2, which contains the homolog of the human jun proto-oncogene, has been genetically mapped and characterized. This project led to the identification and characterization of a Jra (jun-related antigen) mutation, which has been described in detail elsewhere. Three mutagens, EMS, DEB and gamma-rays, were used to isolate 126 lethal lines for this interval. Complementation analysis of the 126 lethal lines identified 29 lethal complementation groups in the region; nine of which have now been correlated with known genes or phenotypes. The region has been subdivided into ten intervals using various small deletions, seven intervals in 46C/D and three intervals in 46E/F. Sixteen P-element lines have been mapped to this interval and are allelic to eight of our complementation groups. The remaining unidentified complementation groups have been analyzed for critical phase, which is when the first observable defect arises and/or when death occurs. There are twelve embryonic lethal groups and seven larval lethal groups. Three lines show visible abnormalities in gut and tracheal development prior to death.