Kinetics of precipitation of-monodisperse samples (degrees of polymerization x : = 11, 12, and 13) of uncharged poly[S-(carboxymethyl)-L-cysteine] was measured at 25 +/- 1 degrees C in salt-free solutions at pH 2.20 +/- 0.02 as functions of molar affinity phi (=RT 1n(C-t/S)) of the reaction, with C-t and S denoting the initial concentration and the solubility. The induction time t(p) was shorter for longer chains. Dependence of t(p) on phi was given common to three chains as follows : log t(p) = -(2.9 +/- 0.2)(phi + alpha, where alpha slightly depended on the chain length. A scheme is proposed to account for the result, consisting of the fast pre-equilibrium for trimer formation followed by the rate-limiting step of the growth of the two-dimensional aggregates through the addition of the trimers, The rate of the addition is proportional to exp(sigma/RT), where sigma represents the surface tension of the trimer. According to the model, the chain length dependence of alpha is given by the rate of detachment of a single chain from the surface of aggregates, which was shown to be very weakly dependent on the chain length in ther present case.