This paper presents the principles of optimal dispatch of heat and electrical power: both the district heating and electrical power systems arc, connected with cogeneration power plants. The cogeneration system with condensing power plants, boiler plants and cogeneration plants with extraction and back-pressure turbines arc considered. The conditions of optimality using Lagrangian function are presented. In addition to the combined optimization of heat and power the three subtasks are, tackled. These subtasks consider the optimal load dispatch in different market conditions. A computer program has been developed.