Dimethyl sulfoxide (DMSO) (1% v/v) stimulated stable transformed Chinese hamster ovary (CHO) cells to synthesize different recombinant proteins and repress their proliferation rate. The expressions of a fusion protein and beta -galactosidase were increased 1.6- and 1.4-fold after adding DMSO. The expression of fusion protein was increased by up to 2.8-fold that of uninduced control by the simultaneous addition of DMSO and pentanoic acid. However, DMSO did not increase the production of the monoclonal antibody (immunoglobulin G) of three hybridoma cell lines (OKM1, OKT4 and HyGPD-YK-1-1), although it could inhibit the growth rates of the hybridoma.