To obtain an insight into the network of cytokine gene transcription in the brain tumour microenvironment, we investigated the expression of genes encoding for interleukin (IL)-1 alpha, IL-1 beta, IL-2, IL-4, IL-5, IL-6, IL-10, interferon (IFN)-gamma, granulocyte-macrophage colony-stimulating factor, tumour necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta 1, -beta 2 and -beta 3 in freshly excised brain tumour samples and autologous peripheral blood mononuclear cells. Tissue specimens from 15 primary brain tumours, three brain metastases, five meningiomas, autologous peripheral blood mononuclear cells (PBMC) and three brain tumour cell lines were tested by reverse polymerase chain reaction. Despite the presence of T-lymphocytes, cytokine gene transcripts typically detectable upon T cell receptor triggering could not be observed in central nervous system tumours of diverse histology. In primary brain neoplasms, transcription of genes encoding for the inhibitory cytokines TGF-beta and IL-10 was detectable in more than 50% of samples. IL-6 transcripts could only be detected in malignant gliomas. In brain metastases, virtually no cytokine gene transcripts could be observed. Surprisingly, TGF-beta transcripts were also detected in all meningiomas. Thus, transcription of genes encoding for inhibitory factors appears to prevail in primary brain neoplasms.