A study was done on organic matter composition of barnyard manure, "purines", i.e., a mixture of solid and Iiquid dejections and food residues, used as organic fertilizer sprayed on soils. Determinations of carbon, nitrogen and phosphorus were made to evaluate manure nutrient contribution and to detect nitrite. Colorimetric techniques were used to estimate the amount of nitrogen and phosphorus-containing compounds. In order to asses the potential use of purines, determinations of pH, density and dry matter were made. Barnyard organic matter fractioning, included in carbon determination, was done to observe the stability and reactivity of organic matter manure. Organic matter contribution in dry matter reached 50 to 60% (2 to 3% of total). This organic matter is quite appropriate because of the balanced percentages of stable and labile, or available, carbono Phosphorus contribution in dry matter varied from 0.6 to 0.9%, which is 26 kg ha-1 phosphorus in the four applications (150,000 L ha-1 ). The evaluation of nitrites, nitrates and amonium showed that there are no detectable nitrites. This means that purines were stabilized and nontoxic and that the amonium content involved an important contribution of nitrogen equivalent to 88 kg ha-1.