The effectiveness of a liquid ammonium phosphate (10-34-0) was evaluated as a fire retardant on a series of test fires on the Hofmann Forest during the spring of 1972. The liquid ammonium phosphate was dropped from air tankers in unthickened and thickened states. The air drops were made directly on the head of the test fires and indirectly by dropping in front of the head and allowing the head of the fire to burn into the retardant. The results showed that thickened liquid ammonium phosphate is an effective fire retardant when used in direct and indirect attack. Unthickened liquid ammonium phosphate is effective when used in an indirect attack.