Genes involved in the determination and differentiation of segmental identity in Drosophila melanogaster have been identified by genetic interactions with the homeotic genes already known to be required. Many new genes required for transcriptional activation or repression of the homeotic genes have been identified. We have cloned two of the genes required for transcriptional activation and one gene required for trancriptional repression. The two genes required for transcriptional activation encode subunits of the TRAP/SMCC transcriptional coactivator complex. Maternal and zygotic expressions of both genes are required for both segmentation and segmental identity. The new homeotic transcriptional repressor encodes a zinc-finger protein conserved between Drosophila and man.We have also continued our genetic and developmental characterization of the brahma chromatin remodelling complex, which is also required for transcriptional activation of homeotic genes in Drosophila. We have identified cis-regulatory elements in two target genes and have been isolating mutations that specifically disrupt interactions of brahma with these two different target genes.