In recent years there has been an encouraging increase in interest in atopic eczema, particularly in relation to its immune logical aspects, and as a result there have been considerable advances in our understanding of the disease. Nevertheless, the relationship of the immunological derangements observed to the disease remains unclear. This relationship will be the principal subject of this review, which will be published in two parts. In the first, genetic and environmental factors predisposing to atopy and atopic eczema will be discussed, and the role of IgE and the significance of other phenomena in the pathogenesis of atopic eczema will then be considered. In the second part, the evidence that atopic eczema is an allergic disease, or more specifically, a food allergic disease, will be reviewed, and a model for the pathogenesis of eczema will be outlined.