A field test was carried out in different production systems to evaluate the effect of vaccination against swine enzootic pneumonia with an inactivated vaccine. A total of 13,691 pigs of four different genetic origins were used, of which 7,351 were vaccinated and 6,340 were used as controls. The animals were housed in 16 fattening units, in which the 'one-site', 'two-site' and 'three-site' production systems were represented. There were the following statistically significant differences in favour of the vaccinated animals: a 1.89 per cent lower mortality (P<0.001), a 0.09 lower feed conversion ratio (P<0.030), a 3.12 per cent lower cost per kilogram gained in fattening (P<0.031), a 4.02 per cent lower cost per kilogram of carcase (P<0.018), a 3.77 per cent lower cost of feed per kilogram gained in fattening (P<0.012) and a 56.75 per cent lower potential loss of profit per kilogram gained in fattening due to mortality (P<0.001). An analysis of variance of the effects of genetic origin, treatment and production system on the different parameters showed that only the treatment had any statistically significant effect on the percentage mortality (P<0.002), feed conversion ratio (P<0.030), cost per kilogram gained in fattening (P<0.019), cost per kilogram of carcase (P<0.020), cost of feed per kilogram gained in fattening (P<0.015) and potential loss of profit per kilogram gained in fattening due to mortality (P<0.002).