Suppression subtractive hybridization (SSH) was used to construct a complementary DNA library enriched for transcripts more abundantly expressed in the resistant BS90 strain of Biomphalaria glabrata at 12 hr postinfection with Schistosoma mansoni as compared with the susceptible M-line strain under the same circumstances. One hundred and twelve clones of the library were sequenced, yielding 88 unique SSH–expressed sequence tags (ESTs). Differential expression screening indicated that 22 of the 88 unique transcripts were strong candidates for differential expression in the BS90 strain relative to the M-line strain. Analysis of a subset of 4 transcripts using quantitative reverse transcriptase–polymerase chain reaction (qPCR) substantially supports the patterns obtained using the differential expression screen. Furthermore, the qPCR results revealed that gene upregulation in resistant snails, downregulation in susceptible snails, and differences in constitutive gene expression can all account for differential expression during the defense responses of resistant and susceptible snails. The majority (71.6%) of the SSH-ESTs recovered consisted of novel sequences not identified by sequence similarity to known genes. This work complements previous efforts to elucidate the genetic components underlying a successful response to S. mansoni by B. glabrata and identifies a series of transcripts deserving additional study in comparing susceptible and resistant snails.