Since the pioneering work of Jelley and Scheibe, it has become a widely accepted fact that the cationic dyestuff pseudoisocyanine chloride (PIC) forms large, chainlike aggregates in aqueous solutions. In the present investigation, the onset of this aggregate formation was investigated by means of time-resolved static light scattering. Water with 0.01 N NaCl was used as the solvent. Aggregation was induced by a temperature drop below the aggregation threshold or by increasing the PIC concentration at constant temperature under equilibrium conditions. In all cases, linear particles with a radius of gyration of 180 nm < R-g < 210 nm have been observed. Results could successfully be interpreted in terms of the wormlike chain model from Kratky and Porod. The Kuhn segment length was l(k) similar to 500 nm being close to the overall contour length of the aggregate chains. A significant growth was observed only for the averaged molar mass and linear mass density of the aggregates. The results are related to an adequate pattern of particle formation and evidence is provided that these particles are the major constituents of PIC gels.