  We present an experimental study of the magnetic flux dependence of the
critical current of a balanced SQUID with three Josephson junctions in
parallel. Unlike for ordinary dc SQUIDs, the suppression of the critical
current does not depend on the exact parameters of the Josephson junctions. The
suppression is essentially limited only by the inductances of the SQUID loops.
We demonstrate a critical current suppression ratio of higher than 300 in a
balanced SQUID with a maximum critical current 30 nA.
