The natural time of differentiation of epidermal cells of cotton ovules into fiber initials, has to be known, in order to influence the differentiation. Our estimates to date indicate that in G. hirsutum, var. Acala Si-2, initiation occurs two or three days prior to anthesis. Preliminary data concerning estimation of the time of fiber initiation will be reported. In vitro methods were used to study changes in development of pre-anthesis ovules and changes in the response of the epidermal layer to light. In vivo changes in the growth regulator, ABA, were assayed by enzyme immunoassay (EIA). Developmental changes in extant proteins were assayed by two-dimensional electrophoresis.