As part of the information needed for applied research on hybridization of these economically important species, the vegetative and reproductive structures ofEucheuma denticulatum (Burman) Collins and Hervey, andEucheuma alvarezii Doty being farmed in Danajon Reef, were studied. All cultured ‘strains’ suspected to have developed from original stocks apparently introduced into the area about twelve years ago were sampled monthly from February 1987 to November 1988. Analyses of fresh free-hand and plastic embedded sections revealed the sexual (male, female) and asexual (tetrasporic) structures inE. alvarezii var.tambalang Doty and the absence of the female inE. denticulatum, indicating the suitability of the former species for future manipulative experiments.