Cells of Distyostelium discoideum representing four developmental stages were auto-analysed for constituent monosaccharides and their compositions compared. Rhamnose, ribose, fucose, glucose, mannose, galactose, glucosamine, galactosamine and an unidentified sugar were recovered after hydrolysis in 2 M HCl for 2 h at 100 degrees C. The relative proportions of the individual sugars were found to vary as a function of development. The largest variations were in the proportions contributed by galactose (from 2% of vegetative cell carbohydrate to 12% of the carbohydrate of fruiting bodies) and galactosamine (present in measurable quantity only in fruiting bodies). Plasma membrane "ghosts" were found to have the same monosaccharide constituents as whole cells, but in different proportions. Mannose contributed over 24% of the total carbohydrate recovered from aggregating cell "ghosts", but only 13% of carbohydrate recovered from "ghosts" prepared from vegetative cells. Galactose was the most abundant sugar recovered from vegetative "ghosts", and was second only to mannose in aggregating "ghosts".