Two-color NPM-ALK FISH assay of (A) a normal metaphase chromosome preparation illustrating the hybridization pattern of the ALK (red) and NPM (green) probes to normal chromosomes 2 and 5, respectively, and (B) a metaphase preparation from a t(2; 5)-positive LCL showing the paired red and green, or yellow fusion, signals present on the der(5) produced by the translocation, in addition to the nonpaired green or red signals present on the nonrearranged chromosomes.