Attention is drawn to the confused epidemiological picture experienced in investigating outbreaks of salmonellosis due to multiple serotypes. Public Health Laboratories are often faced with the examination of specimens containing several serotypes and in this paper six techniques are described which have been found useful in dealing with this problem. The choice of technique depends on the time available for the examination and the epidemiological importance of obtaining an accurate result. A preference is expressed for an immuno-isolation technique, in which the bacteriologist is in technical control of the isolation of specific serotypes. The method is possibly open to objection on the grounds of serological induction of new serotypes, but we should regard this danger as slight in the majority of samples examined.