A monoclonal human anti-soluble schistosomal egg Ag(SEA) antibody (E5) that stimulates anti-Id T cells and is idiotypically represented in pools of immunoaffinity-purified human anti-SEA antibodies from chronic, generally asymptomatic, intestinal (INT) patients (AM1 and AM5) was used to raise several monoclonal anti-Id: 1C2, 1C6, 4A8, 4F9, and 2A7. Cross-inhibition between these anti-Id identified distinct idiotopes on E5. Anti-SEA preparations from schistosomiasis patients (AM1, AM5, and others) were tested for their inhibition of the E5/monoclonal anti-Id reactions, in competitive ELISA. In either the E5/4A8 or E5/1C6 ELISA system, anti-SEA from INT (AM1 or AM5) or hepatointestinal (HI) (AM7) patients were able to inhibit these reactions. However, anti-SEA antibodies from acute (AM9) or hepatosplenic (HS) (AM3 or AM8) patients did not express Id that were inhibitory in these systems. These results suggest that a relatively high proportion of INT and HI anti-SEA antibodies express a dominant cross-reactive idiotope (CRI) recognized by 1C6/4A8. This CRI is also easily detected in plasmas from individual INT patients. Anti-Id 1C2 reacted strongly with an Id in AM1, AM5, or AM7, but one which also occurred, to a lesser extent, in AM3, AM8, and AM9. Monoclonal anti-Id 4F9 and 2A7 reacted weakly with idiotopes expressed by antibodies from all patients, regardless of the clinical form of their infection. These observations indicate that anti-SEA antibodies from INT and HI, but not acute or HS patients express dominant, CRI that are identified by 1C6, 4A8, or 1C2 and are also expressed on the INT-derived anti-SEA mAb E5.