There is a great interest in increasing the efficiency of power generation. In many applications it has been shown that using an ammonia-water mixture as working fluid increases the power output [1-3] (1. Kalina, A., in Second Law Analysis-Industrial and Environmental Applications, ASME AES, 1991, 191, 41.; 2. Kalina, A., in Proceedings of the American Power Conference, Vol. 55-I, 55th Annual Meeting, Chicago, 1993, p. 191; 3. Olsson, E., Thorin, E., Deijors, C. and Svedberg, G., Flowers ＇94, Florence, Italy, 6-8 July 1994.). The Kalina cycle is the best known power cycle that uses ammonia-water mixtures as working fluid. In Sweden, the new power plants being built are direct-fired biomass-fueled steam turbine cycles. They generate power and produce heat for district heating. The plants are quite small, around 100 MWfuel. The aim of the study reported here was to investigate whether there are any thermodynamic advantages of using ammonia-water mixture cycles in small direct-fired biomass fueled cogeneration plants. The main interest is to achieve a higher net power output. The fuel input rate has been assumed to correspond to 80 MW. The district heating network supply temperatures are 90, 100 and 110 degrees C respectively and the return temperature is 50 degrees C. Different configurations of the ammonia-water mixture cycle were compared to a Rankine steam cycle with a five-pressure turbine and three preheaters. Conventional condensing power applications were also studied. Of the three different supply temperatures to the district heating network, the Rankine steam cycle has the highest net power generation. The ammonia-water cycle approaches the Rankine steam cycle when a high supply temperature is desired. For a cogeneration plant without reheat, the difference in net power generation is between 4 and 11%. With condensing power application, the ammonia-water cycle reaches higher power generation than the Rankine steam cycle.