In the present study, the levels of the growth-promoting hormones, somatomedins, were analysed in tumour cyst fluid, CSF, and tumour cytosol, collected from 22 unselected patients with intracranial tumours. All samples contained somatomedin activity. 5/7 CSF samples, taken from patients with tumour mass visible on CT, showed elevated concentrations. 6/9 cyst fluid samples, taken from patients with glioma were elevated compared with normal serum somatomedin levels. Tumour cytosol, taken from 7 patients with malignant glioma contained somatomedins in an elevated level compared with values previously analysed from normal adult brains. These preliminary findings demonstrate for the first time the presence of somatomedins in brain tumours and suggest the use of somatomedins as a possible brain tumour marker.