Holothurians (Holothurioidea, Echinodermata) are known to contain triterpene glycosides, which show antifungal activity. Nevertheless, fungi can be isolated from all organs of holothurians. During 1995-1996, mycelial fungi from several Far-Eastern holothurians—Apostichopus japonicus, Eupentacta fraudatrix, Cucumaria japonica— were collected from the Sea of Japan near the coast of Primorye (Russia) and studied. Twenty-seven species of marine fungi, mostly facultative ones belonging to the mi-tosporic fungi, were isolated from the holothurians and identified. Fungi isolated from the holothurian surface were more diverse and abundant than those from internal organs and coelomic fluids. Of the holothurians studied, Cucum-aria japonica was poorest in abundance and diversity of fungi. The fungi Cladosporium brevicompactum and C. sphaerospermum were common in the holothurian coelom. Because of their high proteolytic activity, these fungi may be pathogenic to holothurians. The detritovorus holothurian A. japonicus was shown to modify the fungal assemblages within the marine bottom sediments.