Solid pig manure (240 g kg1 DM) and solid cattle manure (150-180 g kg1 DM) were stored in an open storage facility during spring-summer and autumn conditions for periods of 9-14 weeks during 1994 and 1995. Concentrations of C, N, P and K were determined prior to and after storage, corrected for dry matter losses and distance from the surface. Temperature and, in experiments with pig manure, gas phase composition inside the manure heap were monitored during storage. Nitrogen losses as ammonia volatilization, nitrous oxide emission and leaching were measured, while total denitrification was estimated from mass balance calculations. For both cattle and pig manure there was little difference between seasons with respect to the pattern of decomposition, as reflected in temperature dynamics and C/N turnover. In contrast, there was a distinct difference between manure types. Pig manure was characterized by maximum temperatures of 60-70°C, although the concentrations of oxygen and methane clearly demonstrated that anaerobic conditions dominated the interior parts of the heap for several weeks. Losses of C and N from pig manure both amounted to c. 50%. In contrast, the temperature of cattle manure remained close to the air temperature throughout the storage period and cattle manure had lower, not significant losses of C and N. Leaching losses of N constituted 1-4% with both manure types. Ammonia volatilization from cattle manure constituted 4-5% of total N, and from pig manure 23-24%. In pig manure a similar amount of N (23-33%) could not be accounted for after storage, a loss that was attributed to denitrification. Nitrous oxide emissions amounted to <2% of estimated denitrification losses.