Aluminium compounds have been widely used as adjuvants in prophylactic and therapeutic vaccines. Adjuvants are able to stimulate the immune system in a nonspecific manner, i.e. high antibody level can be obtained with minimal dose of the antigen and with reduced number of inoculations. Adjuvants use has been mostly empirically determined by such factors as efficacy and safety. The mechanism of action of the aluminium adjuvants is not completely understood and is very complex. The basic factors of the mode of action: 1) the complex of antigen and aluminium gel is more immunogenic in structure than free antigen, 2) effect "depot"--The antigen stimulus last longer, 3) the production of local granulomas. Vaccines adsorbed onto aluminium salts are a more frequent cause of local post-vaccinal reactions than plain vaccines. 5-10% those vaccinated can develop a nodule lasting several weeks at the injection site. In some rare cases the nodules may become inflammatory and even turn into an aseptic abscess. The nodules persisting more than 6 weeks may indicate development of aluminium hypersensitivity. Finally aluminium adjuvant immunogens induce the production of IgE antibodies.