Nuclei of amphibian oocytes contain spheres, either attached at specific loci of lampbrush chromosomes or free in the nucleo‐plasm, the structure and function of which have been investigated for long time. These spheres were initially shown to contain components involved in pre‐mRNA splicing, pre‐rRNA processing and histone pre‐mRNA 3’ end formation. Later, the spheres were labelled by B24/3monoclonal antibody, which recognizes a maternal protein of 104 kDa. Recently, a cDNA clone encoding protein B24has been isolated inTriturus carnifexand analysis of the nu‐cleotide sequence has shown that B24protein belongs to the Mcm/P1 family, which is thought to play an important and conserved role in initiation of DNA replication. To test the function of B24protein microinjections of B24/3mAb were made into one blastomere of two and four‐cell stage embryos. The injected cell degenerated and only hemi‐embryos or underdeveloped embryos were obtained, because B24protein plays an important role in cell division during early development. The results show that the spheres appear as complex accumulation sites of several maternal factors.