During a study of the fine structure of developing conidiophores and spores of Oedocephalum roseum it was found that two kinds of wall growth existed: (a) growth and extension involving addition of wall material, i.e. wall synthesis; (b) extension only, i.e. growth without synthesis but involving instead plasticizing of the wall. The latter type of growth occurred only during denticle formation. Associated with these two types of growth were two different kinds of cytoplasmic organization. During growth involving extension and synthesis, membrane-bounded vesicles of two different sizes were present, but during growth involving extension alone, only the smaller vesicles were present. Observations of Fomes annosus showed a similar pattern. The implications of the observations are discussed.