An automated solution assay instrument (SAI) based on transmission-corrected gamma-ray measurements has been developed and installed in the Plutonium Processing Facility at the Los Alamos National Laboratory. The instrument was designed for rapid, nondestructive assay of plutonium process solutions over a wide range of concentrations (0.05 to 500 g Pu/i, with 10−4 to 5 g Am/ℓ) and for routine operation by process technicians who lack instrumentation experience. For a 25-ml sample, the precision is <0.8% for concentrations >30 g Pu/ℓ within a 1000-s assay and <1.0% for concentrations >4 g Pu/ℓ within a 2000-s assay. The results of test and evaluation demonstrate that the SAI is a reliable and accurate instrument for assaying plutonium process solutions.