The effects of different electrolytes on the aggregation kinetics and fractal dimensions of aggregates of polystyrene latex particles coated by poly(N-isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) have been studied using dynamic light scattering. Whilst PNIPAM is soluble in water at low temperatures, on increasing the temperature and/or adding electrolyte it adopts a globular conformation and becomes hydrophobic, in comparison to the more hydrophilic PEO. For the PNIPAM-coated latexes, the aggregation induced by various sodium salts was found to decrease in the following order: NaCl > NaBr > NaNO 3 > NaI > NaSCN. This sequence is similar to that found previously for latexes coated by PEO. The concentrations of electrolyte required to reach the same fractal dimension at longer times corresponded to the reverse order. The longer time fractal dimensions were found to increase with increasing electrolyte concentration so that the aggregate structures tended to become more densely packed. All the results can be correlated with the sequential order of the viscosity coefficients B η of the electrolytes studied. For the PEO-coated latex, the fractal dimension was found to be insensitive to electrolyte concentration. With respect to temperature, the fractal dimension changed only slightly between 40 and 47.5°C, but dropped dramatically up to 50°C. The observations have been interpreted in terms of the nature of the interparticle interactions.