Technical progress and accomplishments achieved during external hot gas cleanup (HGCU) testing at the PDU were reviewed with representatives of the US Dept. of Energy Morgantown Energy Technology Center, and a 1987 Program Test Scope was finalized for continuation of PDU tests. The major modification for the next test includes reducing the inside diameter of the external desulfurizer from 4.5 to 2.0 feet which will decrease the bed volume to approximately 18 cubic feet. Thus, the time increment required to achieve sulfur breakthrough of the zinc ferrite desulfurizer bed should be less. Another modification removed the cold wall pipe as a gas cooling and deposit control device at the gasifier exit and added a direct water injection system to cool the product gas. In line with the new test scope, modifications were defined for future tests, such as: the option to test ceramic filter elements in the HGCU filter vessel and the addition of a building on the PDU that will house advanced instrumentation to monitor, record, and characterize the trace contaminants in the hot gas exiting the desulfurizer.