Hemolymph lectins may play an important role in the internal defense responses of gastropods to parasites. Two groups of known carbohydrate-binding polypeptides, of 150-220 kDa (designated as group 1 molecules, or G1M) and of 75-130 kDa (group 2 molecules, or G2M), were harvested from pooled plasma samples of Biomphalaria glabrata using affinity chromatography and examined using 2-dimensional electrophoresis. Plasma samples were derived from control snails or snails exposed 8 days earlier to the trematodes Echinostoma paraensei or Schistosoma mansoni. Plasma of control and S. mansoni-exposed snails contained little or no G1M, whereas plasma from E. paraensei-infected snails contained G1M covering a broad pI spectrum. G2M resolved as 1-2 isoforms in control plasma and up to 4 relatively faint isoforms in plasma from S. mansoni-exposed snails, and as 5-6 resolvable isoforms in plasma from E. paraensei-infected snails. Plasma from individual snails contained as many as 5 G2M polypeptides following exposure to E. paraensei. Exposure to trematode larvae stimulated production by B. glabrata of increased abundance and diversity of carbohydrate-binding proteins. The 2 trematode species provoked different responses, and 2 B. glabrata strains studied (M line and 13-16-R1 strains) differed from one another in their responses.