Histones from Anopheles albimanus adults were prepared by a combination of techniques including chromatin isolation and selective extractions. 2. The anopheline histones were identified on acid urea gels by comparing their electrophoretic profile with that of calf thymus histones and histones isolated from other tissue. 3. Excellent separation of histones was obtained after the extractions by a single electrophoretic run. 4. In addition to the five major classes of histones found in eukaryotes, a sixth class was detected and tentatively identified as histone H5. 5. This is the first report of histone H5 and its function in insects.