Cotton fibres are differentiated from single cells of the outer epidermis of ovules and originate at, or soon after, anthesis (Ramsey and Berlin, 1976). Cotton fibre differentiation, characterised by a precise and synchronous growth and uncomplicated by cell division, is a suitable experimental system in which to study cellular and developmental events. In addition, the commercial desirability of long fibres has stimulated studies of the factors involved in controlling the extent of fibre growth. The main aim of this project was to isolate and characterise cDNA clones of mRNAs which are specific to, or important in, cotton fibre development.