A cDNA encoding a lysozyme expressed specifically in the salivary glands of the malaria vector mosquito, Anopheles darlingi, was isolated by differential screening an adult female salivary gland library with abdomen and salivary gland cDNAs. The primary nucleic acid sequence of the cDNA contains a deduced coding region of 429 nucleotides and 5'- and 3'-end non-transcribed regions. A signal peptide of twenty-three amino acids and a mature protein of 120 amino acids are evident in the conceptual translation product. The results of RT-PCR experiments indicated that in adult mosquitoes this gene is expressed specifically in the salivary glands. Lysozyme enzymatic activity was detected in the salivary glands and abdomens of adult mosquitoes, but the pH optimum differed for each tissue and this was interpreted to indicate the presence of more than one enzyme, each being expressed in a different tissue. The salivary gland lysozyme may be involved in protection against bacterial infection in the anterior portion of the mosquito digestive tract.