Glioblastomas are generally thought to be more common in men than in women. In order to investigate the hormone-dependence of these tumours, we established a human glioblastoma line in athymic mice. The tumour cell type was characterized using immunocytochemical methods. The influence of host sex on growth was evaluated, and hormone receptors were characterized biochemically. The histological features of the initial tumour were conserved in the hetero-transplanted tumours, which consisted of vimentin and GFAP immunoreactive astrocytes. There was a highly significant difference in tumour growth between the two sexes (P less than 0.01). In the male mice, tumours were from 2.5 to 10 times larger than in the females, the latency periods were 30% shorter, and the growth phases were characterized by periods of slow or zero growth. In addition, androgen and oestrogen receptors were detected at low levels (80-270 fmol/g tumour) in the heterotransplanted tumours especially in the males. The fact that the male tumour growth profiles resembled those of some hormone-dependent lines, and that androgen receptors were found preferentially in the male rather than in female tumours would tend to indicate that there is a hormonal influence on the growth of the heterotransplanted tumours. These results provide further evidence for an influence of sex-steroid hormones on the growth of glioblastomas.