Coates et al. (1985) have shown that the association reaction of actin with myosin subfragment 1 (Si) consists of at least two steps following the formation of a collision complex; K0 K1 K2 A+ M r--ý AM e-ý A-M c--ý AM The influence of monovalent anions, ionic strength, organic solvents, nucleotide and temperature on this reaction is examined by various kinetic techniques (stopped flaw, pressure junp and slaw temperature jump). Increases in ionic strength above O. 1M, the presence of ethylene glycol or dimethylsulphoxide or the addition of nucleotide reduce K2. In contrast, KoKl is relatively unaffected by these treatments. However, specific monovalent anions above O. 1M do reduce K0 Kl by increasing k_1. The differential effect of these parameters to stabilize actomyosin intermediates for structural analysis is discussed. Geeves & Ranatunga (1990) have demonstrated that high pressure augments twitch tension in intact muscle fibres. Studies of troponin C in solution by pressure jump method show that the binding to calcium is not affected by 100atm pressure. This suggests, assuming that the effect of pressure is no different to that in fibres, that muscle is "switched on" to a larger extent per stimulus at high pressure by either increased release of calcium fron the sarcoplasmic reticulum or by a change in the inhibitory function of the regulatory proteins. The rate binding properties of fluorescent labelled TnC to calcium are investigated by pressure jump and fast temperature jump methods.