In this study 27 full scale production batches of influenza sub-unit vaccine were evaluated on their stability. The batches varied with respect to the strains they contained and regarding the presence of the preservative thiomersal in the solution. The stability study showed that haemagglutinin content was the most sensitive parameter. An increase in the storage temperature strongly increased the degradation rate of haemagglutinin. The degradation rate of the haemagglutinin differed for the different strains tested. However, statistical evaluation of the data obtained for the most sensitive strain tested showed that even exposure during a 2 week period of the vaccine to room temperature would not adversely affect the shelf life claim of the influenza subunit vaccine of 1 year in the refrigerator. Moreover, this study showed that the presence of thiomersal in the solution has no effect on the stability of the vaccine.