Cleistogamy in Salpiglossis sinuatu L. involves a sequence of events, including arrested corolla development, precocious pollen germination inside anther, pollen tube penetration of the pistil, and eventual self fertilization, that takes place. within a tightly closed flower bud. A single dominant gene (C) controls cleistogamy in this plant. During early blooming period, cleistogamous (CC, Cc) plants produce both chasmogamous (open) and cleistogamous (closed) flowers. Enzymes in various tissues of both cleistogamous and chasmogamous buds were detected by isozyme banding patterns in starch gel electrophoresis. The onset of cleistogamy may be signalled in the calyx and corolla tissues in the early stage of flower development. The levels of specific enzymes (PGM, PGI, G-6PD, PGD, MPI) involved in gluconeogenesis, pentose phosphate shunt and glycolysis in both calyx and corolla tissues of the cleistogamous buds were greatly reduced. These enzymes were present in the pistil and anthers of cleistogamous buds and in all floral parts of the chasmogamous buds.