A lectin with a high affinity for glucose/mannose was isolated from Annona muricata seeds (Annonaceae) by gel filtration chromatography on Sephacryl S-200, ion exchange chromatography on a DEAE SP-5 PW column, and molecular exclusion on a Protein Pak Glass 300 SW column. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (PAGE) yielded two protein bands of approximately 14 kDa and 22 kDa. However, only one band was seen in native PAGE. The Mr of the lectin estimated by fast-performance liquid chromatography-gel filtration on Superdex 75 was 22 kDa. The lectin was a glycoprotein with 8% carbohydrate (neutral sugar) and required divalent metal cations (Ca2+, Mg2+, and Mn2+) for full activity. Amino acid analysis revealed a large content of Glx, Gly, Phe, and Lys. The lectin agglutinated dog, chicken, horse, goose, and human erythrocytes and inhibited the growth of the fungi Fusarium oxysporum, Fusarium solani, and Colletotrichum musae.