Field-collected and laboratory populations of Anopheles albimanus were analyzed for the presence of variability for the enzyme, peptidase. Four zones of peptidase electromorphs were observed. The Peptidase-4 (Pep-4) locus was analyzed genetically and assigned to a location adjacent to the centromere on the right arm of chromosome 2 by employing crosses involving morphological mutants, allozyme markers, a holandric translocation, and pericentric inversions. The gene sequence (and map distances) on chromosome 2 beginning from the left arm Is: brown larva—40—ebony (eb)—centromere—pep-4—?—bent(be)—?—Glutamate oxaloacetate transaminase(Got)—11—Glucose oxidase-2(Go-2)—17—green larva (gl)—9—amber (am)—2—propoxur resistance (prr)—2—red eye (re)—21—6-Phosphogluconate dehydrogenase (6-Pgd)—1—yellow. The crossover frequencies between eb and Pep-4 and Pep-4 and Got were 34 and 16, respectively.