The catalytic activity and selectivity of a series of rhodium(I), (II) and (III) complexes have been examined in a model hydrosilylation reaction of 1-octene with triethoxysilane and in a more applied system composed of oligomeric allyl ethoxylate alcohol and poly(dimethylsiloxane-co-methylsiloxane). The results were compared with the catalytic activity of the widely used Karstedt's system (Pt-2[(ViSiMe(2))(2)O](3) (1)). The tris(3-phenyl,5-methylpyrazol-1-yl)borate (Tp(Ph,Me)) dicarbonyl rhodium(l) compound Tp(Ph,Me) Rh(CO)(2) (2) was found to be more active in both reactions than (1), but in case of hydrosilylation of the polymeric species, (2) was less selective leading to a higher amount of the undesired Markovnikov addition. The catalytic activity of the other rhodium complexes Rh(Hdmg)(2)(PPh)(3)Cl (3), [Rh(Hdmg)(2)(PPh3)](2) (4), [Rh(HdMg)(2)(PPh3)(2)]ClO4 (5), Tp(Ph,Me) Rh(CO)(PPh3) (6), Rh(CH3COO)(PPh3)(3) (7), [Rh(HdM(9))(2)(ClZndmg)(PPh3)](2) (8) (Hdmg = diemthyl-glyoximate) was similar to or somewhat lower than 1. No clear relationship was found between the formal oxidation state of rhodium and the catalytic activity of its complex, which is in contrary to theoretical suggestions. (C) 2003 Elsevier B.V. All rights reserved.