The chronic myelogenous leukaemia cell line K562 can be triggered in culture to differentiate along the erythrocytic pathway in response to a variety of stimulatory agents. In the presence of sodium butyrate, these cells differentiate to erythroblasts and acquire the capability to synthesize haemoglobin. We used this cell system to study alterations in the levels of several G-protein subunits during the cell differentiation programme and to assess the involvement of G(i)alpha2 in this process. Western immunoblot analysis revealed the presence of G(s)alpha1, G(s)alpha2, G(i)alpha2, G(q)alpha, Galpha(12), Gbeta1 and Gbeta2 in K562 cells. G(o)alpha, G(z)alpha, Galpha(13) and Galpha(16) were not detected. Although the levels of several G-protein subunits were altered after treatment with sodium butyrate, the most striking change was the robust increase in the levels of G(i)alpha2, which was accompanied by an increase in the mRNA for G(i)alpha2. Inactivation of G(i)alpha2 by adding Bordetella pertussis toxin to the cultures inhibited erythroblastic differentiation by as much as 62%, as measured by haemoglobin accumulation. Furthermore, the addition of an oligonucleotide anti-sense to G(i)alpha2 inhibited the sodium butyrate-induced robust increase in G(i)alpha2 levels, decreasing it to the basal levels seen in control cells; this treatment decreased the erythroblastic differentiation of the cells (as measured by haemoglobin expression) by 50%. Taken together, these findings imply that increased levels of G(i)alpha2 contribute to the sodium butyrate-induced erythroblastic differentiation of K562 cells.