A four-component vaccine, prepared by combining the single vaccines, contains subunits of Newcastle disease and infectious bronchitis viruses, as well as whole inactivated infectious bursal disease and egg drop syndrome viruses. The vaccine is prepared in the form of a low-viscosity water-in-oil-in-water emulsion with low mineral oil content. Heavy breeders were vaccinated at the age of 20 weeks by intramuscular administration of 0.5 ml vaccine/bird in an experiment carried out under field conditions, involving 5000 female and 450 male parents. The birds had previously been vaccinated with live vaccines according to an obligatory field vaccination programme. Vaccination with the WOWE vaccine near the point of lay elicited serological responses protecting both the parents and their progeny. Each of the antigens administered in the four-component vaccine was as effective as the respective single component vaccine. The mortality, recorded during the 31-week experimental period, was 6.2%. Mortality and morbidity were not triggered by viruses against which vaccination was carried out. Egg production was not affected by the vaccination and was 170.2 eggs per hen during the 28-week production period.