Wyner and Ziv considered the problem of source encoding and decoding when the decoder knows a random variable

correlated with the source

. The least rate

for which the system can operate with fidelity

ia given ia terms of an information theoretic minimization

. Explicit upper and lower bounds to

are given for an important class of correlated sources. The upper and lower bounds have been evaluated for several members of the class and are shown to agree in these cases.