By acidification of liquid cattle manure in the pit underneath the floor, the emission of ammonia from an animal house can be reduced. Two systems for acidification can be distinguished: 1) Acidification with sulphuric acid; 2) Biological acidification, i.e. acid compounds are produced by bacteria in the manure. At the request of the Dutch Ministry of Economic Affairs in this report the main aspects of these systems are discussed. The analysis shows that the maximum achievable ammonia emission reduction is about 20%. Applied as a single low-emission measure in dairy barns, this reduction is not large enough to comply with the maximum levels that will come into effect from 2018, implying that this measure has to be combined with additional techniques, such as low-emission floor or air scrubbing techniques, and as such restricting perspectives for practical application. Furthermore, it is concluded that the sulphuric acid acidification system is ready for on-farm implementation, whereas the biological acidification system needs to be further developed. Acidification with sulphuric acid leads to a drastic increase of the sulphur content of the manure; attention must be paid to maximum sulphur application rates when this manure is applied to the soil; when this system is applied to the soil. The operating costs for biological acidification are about twice as much as for acidification with sulphuric acid. Besides, application of biological acidification might lead to a higher methane production. Because of the relatively high costs, it is uncertain whether biological acidification is feasible, even when it is ready for practical implementation. Therefore it is concluded that the biological acidification system is without prospects for the short term. The economic feasibility might improve when the increased methane production can be used in a digester. It is recommended to further study the feasibility of a combined system of biological acidification and manure digestion.