The role played by the seed coat in seed dormancy of Grevillea linearifolia (Cav.) Druce and G. wilsonii (A. Cunn.) was tested by a series of manipulations in which the seed coat was dissected and removed, dissected and returned to the decoated seed, or dissected, removed and given a heat shock, and returned to the decoated seed. Germination of intact seeds of both species was also examined after exposure to heat shock, smoke, or heat shock and smoke combined. Water permeability of the seed coat was investigated by examining imbibition. For intact seeds, virtually no germination occurred under any treatment (G. wilsonii), or germination was increased by exposure to either heat or smoke (G. linearifolia). Removal of the seed coat led to germination of all decoated seeds for G. linearifolia, or a proportion of decoated seeds for G. wilsonii. Inclusion of smoked water in the incubation medium led to a higher proportion of decoated seeds germinating for G. wilsonii. Returning the seed coat, either with or without heat shock to the seed coat, did not significantly affect germination in either species. Seed coats were permeable to water in both species. For the two Grevillea species, there were different dormancy mechanisms that were controlled by the seed coat (G. linearifolia) or by both the seed coat and embryo (G. wilsonii). © 2000 Annals of Botany Company.