This review covers: acute toxaemic schistosomiasis; pathology of chronic human and experimental schistosomiasis; immunopathogenesis of circumoval granulomas (role of cytokines in granuloma formation with Schistosoma mansoni, role of cytokines in granuloma formation with S. japonicum, immune downregulation of the granulomatous response during chronic S. mansoni infection, immune modulation results from an active suppressor-cell mediated process, putative mechanisms of immune modulation-utility of the T1/T2 paradigm, properties of CD4+ helper cells in the chronic, modulated infection, immune downregulation of the granulomatous response during chronic S. japonicum infection, clinical disease correlates with the failure to develop downregulatory mechanisms\); fibrotic reactions induced by schistosome eggs.