Ethene was copolymerized with 1-decene and 1-hexadecene in the presence of heterogeneous MgCl2/TiCl4-triethylaluminum catalyst to study the effect of adding 1-butene to the polymerization system. When 1-butene concentration in the feed was increased from 0 to 0.4 mol/dm3, 1-decene content in the polymer increased 2-fold. Further addition of 1-butene has no effect. The more reactive the added comonomer, the more it increased the ethene consumption. Ethene was also copolymerized with 1-octadecene in the presence of Cp2ZrCl2-methylaluminoxane catalyst. Surprisingly, 1-butene addition decreased the reactivity of the higher alpha-olefin : 1-octadecene content decreased linearly, to one-third, when 1-butene concentration was increased from 0 to 1 mol/dm3. Monitoring of the ethene consumption during the polymerizations showed that the comonomer concentration in the feed has a saturation point, beyond which further addition of comonomer does not increase the consumption of ethene.