Thin-layer chromatography was used to analyze the free-pool amino acids of the digestive gland–gonad complex (DGG) of Biomphalaria glabrata infected with Echinostoma caproni and uninfected (control) snails. Qualitative analysis revealed the presence of histidine, lysine, serine, alanine, valine, and isoleucine or leucine in all samples. Quantitative analysis of lysine and valine gave mean weight percentages of 0.00699 ± 0.0022 and 0.00174 ± 0.00056, respectively, in the DGG of uninfected snails, and 0.00504 ± 0.0014 and 0.00254 ± 0.00033, respectively, in the DGG of infected snails. The differences in values between infected and uninfected snails were not statistically significant (Student's t-test, P > 0.05).