Differentiation of bloodstream-form trypanosomes into procyclics in tsetse flies (Diptera: Glossinidae) is a crucial step in the establishment of midgut infections. A number of factors have been implicated in the transformation process, including enzymes and lectins or lectin-like molecules. Recently, Glossina proteolytic lectin (Gpl) gene, which encodes a protein with both lectin and trypsin activities has been shown to stimulate transformation of bloodstream-form trypanosomes into procyclics in vitro. Using RT-PCR, we show that the induction of Gpl gene expression by blood meal occurs only in Glossina fuscipes fuscipes Newstead, Glossina austeni Newstead, Glossina pallidipes Austen, and not in the Anopheles gambiae Giles sensu stricto, Phlebotomus duboscqi Neveu-Lemaire, Rhipicephalus appendiculatus Neumann and Stomoxys calcitrans (Linnaeus). The expression means of Gpl mRNA in G. f. fuscipes following a blood meal were significant (P < 0.05) with low expression in teneral flies and reaching a maximum between 48 and 72 h (P < 0.05), suggesting time-dependent regulation of the transcription. The expression of the Gpl gene was significantly lower (P < 0.05) in G. f. fuscipes fed on blood meal infected with Trypanosoma brucei brucei as compared with G. f. fuscipes fed on uninfected blood meal. This suggests some form of interaction of T. b. brucei or the parasite products with Gpl within the tsetse midgut leading to down-regulation of the Gpl gene. Additionally, refractory G. f. fuscipes expressed higher (P < 0.05) transcript abundance than the susceptible G. pallidipes.