RESUMO - (Ehrenb.) Fr. was analyzed just before the transplant of these seedlings to the field to ascertain if fungi are established in the roots. Ectomycorrhizal fungi formed a well-developed compact mantle in lateral roots. Vacuoles, nuclei and dolipore septa were observed in mantle hyphae and numerous nuclei, endoplasmatic reticulum and polymorphic mitochondria were frequently located in the cytoplasm of Hartig net hyphae adjacent to plant cortical cells. Highly vacuolated cortical cells contained droplets of electron-dense material, nucleus and some organelles were observed in a narrow region of peripheral cytoplasm. The ectomycorrhizas of P. caribaea var. hondurensis exhibited typical ultrastructural characteristics of a compatible and physiological active association.