Non-cirrhotic portal fibrosis (NCPF) is a common cause of portal hypertension in India. Its aetiopathogenesis is not well understood. To investigate the possibility of an immune mediated injury, phenotypes of peripheral blood lymphocytes were studied in 15 NCPF patients and were compared with an equal number of compensated cirrhotics and matched healthy controls. The population of total peripheral T lymphocytes (T1) and suppressor/cytotoxic phenotype (T8) was significantly (P less than 0.01) decreased in NCPF patients compared with controls. The sub-populations of helper/inducer lymphocytes (T4) and total B lymphocytes, however, were comparable with controls. The ratio of T4 to T8 lymphocytes was significantly (P less than 0.01) increased in NCPF patients in comparison with controls. Similar changes in the lymphocyte population were also observed in cirrhotic patients. Further investigations are required to identify whether the cellular alterations seen in NCPF have a pathogenetic basis or are secondary to the disease process itself.