Preservatives have come under fire due to their possible detrimental properties and the high rate of contact allergies some of them cause. Therefore, the pharmaceutical industry is searching for alternatives that will be effective, safe and economical. The present paper introduces a selection of new or revived biocides (Kathon CG, benzisothiazolinone, Euxyl K 400, Biobans, Grotans, Bronopol, Germall II), and the range of application and the sensitization potency of each are discussed. Test concentrations for patch tests are recommended. Kathon CG is the most commonly used preservative among these biocides, although it has a high sensitization potency and is a frequently encountered contact allergen. To make discovery of a new allergen easier and to reduce the risk of side effects, manufacturers should be required to specify the ingredients of their products on the labels.