The ratio of the concentrations of κ- to λ-carrageenan is shown to be related to the nuclear phase in Chondrus crispus both in culture and in nature. This ratio is low in tetrasporic plants and relatively high in the gametophytes. It was found to vary somewhat amongst samples analysed, but was always less than unity in tetrasporophytes and greater than unity in gametophytic plants. The κ/λ ratio in Gigartina stellata was high in gametophytes as in C. crispus; the tetrasporophytic phase of this species is unknown. It is suggested that the commercial quality of carrageenan can be correlated with the biological status of the harvested plants.