We describe a procedure for delivery of purified proteins into a variety of tissue culture cells using a new polycationic lipid preparation, LipofectAMINE. Several different proteins, with diverse physical properties, can be delivered into cells by this method. Compared with commercially available monocationic lipids, protein delivery using LipofectAMINE is more efficient. Unlike other methods for protein delivery, the lipofection procedure is simple, inexpensive and effective for both adherent and nonadherent cell types. Proteins introduced into cells using this method are shown to be biochemically and biologically active.