Organic rest after processing within the biogas plan operation do not pollute the environment and may be used as a first class fertilizers; and additionally they can be used as biogas in cogeneration operation of head and current, in which case one head of cattle would provide at least 1.7 kWh of electrical energy and 3.4 kWh of heat each day. In such cases that the pig`s manure is being released unprocessed from a farm operation into the ecological environment; and for the heating generation on the farm one of the standard unrenewable fuels is being consumed, a double harm has been effected - one that can be measured and the other which can not even be estimated: pollution of fresh air, water and flora life supply. In a careful estimate Austria provides premises for 40000 biogas processing plants which would generate 3.6 Billion kWh of electric energy within the cogeneration operations. What about Croatia? (author). 4 figs., 2 tabs., 6 refs.