The efficacy of spray vaccination against Infectious Bronchitis (IB) in rearing layers, was examined in 12 flocks housed on 2 farms. For this purpose the vaccine was prepared with substantially more water than is commonly used in practice and was carefully sprayed in the direction of the animals. Single vaccination at 2 weeks of age resulted in mean 2log HI titres of only 3 to 4 at the end of the rearing period (16 weeks), whereas two vaccinations yielded titres of 6 to 7. Upon a third vaccination, titres increased up to 7 to 9, individually even reaching 11. These titres are distinctly higher than the mean level in the Netherlands. None of the flocks showed clinical symptoms of IB, neither during rearing, nor in the laying period, except one. For unknown reasons, this flock showed a poor serological response after three vaccinations and subsequently experienced clinical IB at the start of the laying period. It is concluded that administration of live IB vaccines as described in this study, deserves large scale practice, because it will then become clear whether this procedure contributes to a better IB prevention or not.