Cytokines are powerful modulators of immune responses, the local production of which could be relevant to the interaction between tumour and immune system. This study investigated the transcription of genes encoding interleukin (IL) 2, IL-4, IL-10 and interferon (IFN) gamma in lymphocyte-infiltrated renal cell carcinoma biopsies from ten patients using the reverse polymerase chain reaction technique. Autologous peripheral blood mononuclear cells and healthy renal parenchyma tissue were tested in parallel. The beta-actin gene, used as a positive control, was transcribed in all samples. In contrast, transcription of cytokine genes was confined to tumour biopsies: IL-2 gene transcripts were detectable in five biopsies and IL-10 transcripts in seven. IL-4 and IFN-gamma gene transcripts were detectable in one biopsy each. In two patients no cytokine gene transcription could be identified. These data underline that heterogeneous patterns of cytokine gene transcription can be observed in renal cell carcinoma biopsies. Although transcription of an immunostimulatory lymphokine such as IL-2 was observed in 50 per cent of biopsies, the most frequently transcribed cytokine gene coded for an inhibitory factor, IL-10.