We have briefly described our studies of cytoskeletal and contractile elements in intact cells, in cell extracts, and in mixtures of purified proteins. Changes in the concentration of calcium and of protons have been found to modulate both gelation and contraction in all of these preparations. The distribution of calcium, protons and actin has been studied in intact amoeboid cells. Using these results, we have refined our working model of the relation of cytoskeletal and contractile proteins: the solation-contraction coupling hypothesis. The model is also supported by quantitative analysis of the rates of contraction in a soluble extract of Dictyostelium discoideum amoebae allowed to gel in a capillary and stimulated by the addition of calcium ions at one end. A plausible interpretation of the most prominent cytological features of amoeboid locomotion is obtained by application of the principles of our model. In addition, we propose that the solation-contraction coupling hypothesis may be useful in further study of a variety of motile phenomena observed in many types of cells.