Methodologies for T and B lymphocyte quantitation, lymphocyte blast transformation (LBT) and carbohydrate (CHO) metabolism are important for assessing host lymphocyte response in the clinical laboratory. Modifications of methods for each of these techniques are presented. Results from studies of normal ambulatory adults, patients with diabetes mellitus, sickle cell disease and hyperlipidemia are reported. LBT of normal lymphocytes before and after ethanol exposure are examined. LBT during pregnancy is evaluated. T cell populations are abnormally high in black diabetics and decreased in patients with sickle cell anemia. B cell subpopulations are increased in patients with sickle cell anemia. LBT responses are decreased in maturity onset diabetes, during pregnancy and in patients with sickle cell disease. Ethanol in amounts attainable during human consumption results in significantly decreased LBT response. CHO metabolism (especially hexose monophosphate shunt [HMPS] and HMPS by pentose sugar recycling) is abnormal in diabetic lymphocytes. The low HMPS activity is partially reversible by treatment with prostaglandin synthetase inhibitors. Information related to lymphocytes in normal states remains to be collected by further clinical application of these techniques of quantitation and in vitro function.