The first event in the formation of a new fungal colony is the germination of a spore, which is one of the most crucial events in the life cycle. The infection of a plant by a parasitic fungus and the resulting production of disease is initiated, in most instances, by a spore germinating within or near the potential host plant. Thus, for plant pathogenic fungi in particular, the elucidation of the spore germination mechanism is likely to be significant in devising strategies for crop protection. Although spore germination is regulated by several physical factors such as temperature, moisture, and light in a favorable environment where water is an indispensable factor, it has been proposed that certain chemical signals also assist or promote spore germination. For example, some chemical components from the host plant may promote conidial germination of parasitic fungi. Despite the lack of direct chemical evidence, it is reasonable in an ecological context that such a promoting factor participates as a chemical signal between the host and the parasite. Spores of some fungi have been shown to contain endogenous self inhibitors which initiate (de-repress) germination by leaching from the spores themselves. In general, mature spores removed from the parent mycelium begin to germinate readily when dispersed in water. However, the percent germination is dependent on the population of spores in several examples. For the strawberry anthracnose fungus, more than 90% germination is observed at 10⁴ spores/ml; germination decreases as the population increases and is almost completely inhibited at 10⁷ spores/ml. Inhibition at high conidial concentration is not reduced by addition of O₂ but is depressed by washing the conidia with water to remove exudates. Repeating the washing procedure at 2×10⁶ spores/ml increases germination from 20% to 80%. Induction of germination by washing suggests germination inhibitor(s) exuded into the environment at high concentrations under dense conidial populations. Germination under dense conditions is disadvantageous for survival due to nutrient competition during vegetative growth, so the inhibitor functions to retard germination until a favorable environment is encountered. This exuded inhibitor is likely an endogenous factor in conidia regulating germination, easily exuded under moist conditions, and removed by washing to initiate germination, regarded as a fungal hormone or endogenous factor controlling spore quiescence. Self-inhibition of germination has been observed in over 60 examples. Early studies by Allen showed a regulatory substance (germination self inhibitor in water extracts of uredospores) is important for uredospore germination of Puccinia graminis f. sp. tritici. Macko later elucidated the structure and isolated native self inhibitors in several fungi. These self-inhibitors exhibit sporostatic activity at extremely dilute concentrations, with reversible and specific effects (only inhibiting spore germination, not hyphal growth). Characterization of self inhibitors may provide new targets for antifungal agents, and analyzing their mode of action may disclose the mechanism of release from dormancy to germination in fungal spores and higher plant seeds. In this article, advances in the chemical characterization of self inhibitors are described from the perspective of natural product chemistry.