An ATP-independent strand-transfer activity has been identified in nuclear extracts prepared from Drosophila tissue culture cells and isolated nuclei from Bombyx testes. Extraction of the activity from testes at larval stages where the majority of the cells were in meiotic prophase was only possible when the chromosome scaffold/synaptonemal complex was dissolved by addition of high concentrations of DTT (80 mM). No cross reaction was detected when partly purified extracts were assayed with antibodies against E. coli RecA protein.