A panel of T-cell clones reactive to the soluble egg antigen (SEA) of Schistosoma mansoni is described. The proliferative responses of the primary immune lymph node (LN) cells and T-cell clones to different schistosome antigen preparations (cercarial extract (CE), live or dead schistosomula, adult worm extract, and soluble egg antigen) were compared. Primary immune LN cells could not distinguish between these schistosome antigen preparations. However, when a total of 22 T-cell clones was analysed, a complex pattern of both stage-specific and common (or cross-reactive) antigen reactivity was observed. These patterns have been grouped into four types: (i) five clones were reactive to all different schistosome antigen preparations; (ii) two clones were reactive only to SEA, CE and schistosomula; (iii) three clones were reactive only to SEA and cercariae; (iv) twelve clones were reactive to SEA antigen alone. The T-cell clones were identified as Thy-1-positive cells. All the clones were able to respond to exogenous IL-2 after antigenic stimulation. However, there was a variable degree of IL-2 responsiveness when compared with antigen-specific stimulation. Four T clones were selected for further studies on the genetic control of the proliferative response to schistosome antigens. One of the proliferative T clones was restricted by the IA subregion of the major histocompatibility complex (MHC), and the other three clones are restricted by the IE (AeE alpha) subregion.