The presence of low concentrations of methanol or isopropyl alcohol (2-5%, v/v) in the assay medium stabilizes the latency of dynein 1 from sea urchin sperm flagella, with about a 50% decrease in ATPase level compared to that in the absence of solvent. Somewhat higher concentrations (10-20%, v/v) of these solvents in the assay give a 5-10-fold activation of ATPase activity. Dioxane, formamide, and dimethylformamide, on the other hand, always activate the ATPase activity, with a 5-10-fold increase observed at about 15% (v/v). The activation of latent ATPase activity by solvents is reversible for short exposures, especially in the presence of ATP and at low temperature, but the activation becomes irreversible upon more prolonged exposure. The rate constant for irreversible activation by 16% methanol at 21 degrees C is 0.08 min-1, compared to rates of 0.44 and 0.02 min-1 for activation by 0.05% Triton X-100 at 21 and 0 degree C, respectively. The slowness of this reversible activation induced by methanol and by Triton X-100 suggests that it is the result of large-scale conformational changes in the structure of the dynein. However, the activation by methanol occurs without the dissociation of the alpha and beta subunits of dynein that is observed with Triton X-100. The presence of 1 mM MgATP, or of 100 microM MgATP and 10 microM vanadate substantially protects latent dynein from activation by 0.05% Triton X-100.