The aggregation of 5-dodecylsalicylaldoxime, 5-nonylsalicylaldoxime and two long chain alcohols, 1-tridecanol and isotridecanol-N (components of the commercial extractants LIX 622 and LIX 622N) in toluene and n-heptane has been studied by vapour pressure osmometry. Osmometric data have been treated numerically and the results reveal the formation of dimeric species for the salicylaldoxime derivatives in toluene at 301 K. Dimerization constants are reported. The tridecylalcohols studied dimerize in toluene whereas in n-heptane form aggregates of three and four molecules. The corresponding aggregation constants are proposed.