Growth inhibitory activity of recombinant alpha and beta interferon on two human glioma cell lines, EFC-2 and KE cells, was determined by two different growth assays. Recombinant beta interferon showed a slight growth inhibitory effect on EFC-2 cells at day 3, and maximum inhibition was seen on day 6 with an ID50 of 50 U/ml. Recombinant alpha interferon showed no significant growth inhibition at any concentration. KE cells were resistant to both recombinant alpha and beta interferon. The growth inhibitory activity of recombinant beta interferon on EFC-2 cells was not blocked by recombinant alpha interferon, although recombinant alpha and beta interferons shared same receptors on EFC-2 cells. Addition of DFMO (alpha-difluoromethylornithine) to interferon in the media showed additive effect rather than synergistic effect in growth inhibition of glioma cells. Out of 7 glioma cell lines tested, 4 showed heterogeneous sensitivity to recombinant beta interferon, and all were resistant to recombinant alpha interferon. These results suggest a differential sensitivity of EFC-2 cells to recombinant beta interferon, as well as a heterogeneous sensitivity to recombinant beta interferon among different glioma cell lines.