The motility of individual, aggregation-competent amebae of Dictyostelium has been analyzed at different concentrations of cAMP under both nongradient and gradient conditions. The following is demonstrated: (a) concentrations of cAMP greater than 10(-8) M inhibit motility in a concentration-dependent fashion, decrease the frequency but not the degree of turning, and cause rounding in cell shape; (b) no concentration of cAMP stimulates motility, or positive chemokinesis; (c) concentrations of cAMP that stimulate a maximal chemotactic response do not affect motility and concentrations of cAMP that maximally inhibit motility do not stimulate chemotaxis under gradient conditions; and (d) the concentrations of cAMP that inhibit motility are identical under gradient and nongradient conditions.

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