The first physics measurements for a heterogeneous design of a 1000-MW(thermal) liquid-metal fast breeder reactor were made in the Zero Power Plutonium Reactor (ZPPR) during the last half of 1976. This benchmark assembly, ZPPR-7, had a central blanket zone as well as three internal blanket rings. Fuel zones had a single enrichment. Cores with heavy plutonium buildup in the internal blankets as well as cores with clean internal blankets were investigated. Such key physics parameters as keff, most of the important reaction rates, control rod worths, sodium void reactivity, and material worths were studied in the ZPPR-7 program. Results verified the gain in breeding that were predicted for the heterogeneous arrangement. When design-level calculations were used, calculated-to-experimental biases were different from those that had been found for homogeneous cores.