The 210H/MspI system identified six standard fragments in the core cell lines as shown in Table 1 and Figure 1. Much of the data received for this system was difficult to interpret because all the fragments were of low molecular weight and thus produced indistinct bands. High background on several autoradiographs was also a contributory factor in the discrepancy between duplicates in the first fragment. Only fragments 1 (1.27 kb) and 4 (0.49 kb) were found to be polymorphic.