A new one-step method for SCE visualization after BrdU incorporation, using prolonged hydrolysis and the Feulgen reaction, has been developed. InVicia fabait gives essentially the reserve of the FPG technique with darker stained double-substituted chromatids. Besides harlequin chromosomes, the new method reveals bands in the approximate position of known heterochromatic segments, and also asymmetric bands after one round of replication in the presence of BrdU.