Spheroids initiated directly from human primary gliomas were used to investigate the effects of EGF, bFGF, NGF and PDGF(bb) on cell proliferation, migration and invasion into foetal rat brain tissue. EGF increased tumour spheroid volume in 10 of 13 glioblastomas studied, whereas 5 of 11 tumours responded to bFGF. NGF increased the spheroid volume in 2 of 5 tumours. In 8 tumours, PDGF(bb) had no effect on tumour spheroid volume. An increase in BUdR-labelling indices confirmed that cell proliferation was responsible for the volume increase observed in stimulated spheroids. EGF stimulated cell migration in 5 and bFGF in 3 of 8 tumours studied. NGF stimulated cell migration in 1 of 5 glioblastomas, whereas 1 of 3 glioblastomas responded to PDGF(bb). The effects of growth factors on the invasion of spheroids prepared from the glioblastoma biopsy specimens were also studied in vitro using foetal rat brain aggregates as target tissue. EGF stimulated invasion in 7 of 8 glioblastomas studied, whereas bFGF stimulated invasion in 2 of these tumours. NGF or PDGF(bb) did not increase the invasiveness of the glioblastoma tissue. Our results represent the net effect of the growth factors on a complex tumour-cell population. We conclude that exogenously administered growth factors, EGF in particular, increase the cell proliferation as well as migratory and invasive capacities of cultured primary brain tumour biopsies in vitro.