We generated and characterized a new hypomorphic mutation of Drosophila melanogaster Trithorax-like (Trl) gene named Trl362 . The Trl 362 homozygous females are sterile and lay a small number of eggs; most embryos die at the early developmental stages. The transcriptional Trl level of adult Trl362 females was markedly lowered. Little or no GAGA protein, encoded by Trl, was detected in the nurse cell nuclei. The ovaries of Trl362 females showed impairments, such considerable changes in the structure of both ovarioles and individual egg chambers. We believe that the observed ovarian defects in Trl362 mutants are mostly due to a decreased amount of GAGA protein in the germline cells. An increase of GAGA-519 protein caused by introduction of hsp83:GAGA-519 transgene against Trl 362 background rescued partially the female fertility. It may well be that a decrease of GAGA protein in Trl362 germline cells leads to a defective expression of the genes regulated by transcription factor GAGA, whose products are essential for normal Drosphila oogenesis.