The study is designed to develop novel assays for the differential diagnosis of human Chronic Myelogenous Leukemia (CML). The basic method involves the use molecular techniques to detect the Ph1 chromosomal translocation. Hybridization with a labeled DNA probe identifies novel junctions between the cellular abl proto-oncogene, from chromosome 9, and the phl gene from chromosome 22. In CML the junctions occur with small breakpoint cluster region (bcr), and can be detected readily in genomic DNA. Assays based on the detection of novel junctions in messenger RNA also will be developed. Clinical evaluation of the assays, in comparison with cytogenetic analysis, will be completed. The assays have commercial application as a clinical laboratory test for the diagnosis and monitoring of leukemia patients.