1.   In discordant ulcerative colitis twin pairs, no difference appeared in the cellular IgG subclass pattern between healthy and affected twins.

2.   The distribution of twins in concordant and discordant twin pairs, and the number of twins with an ileostomy, are shown in Table I.

3.   In the study of serum immunoglobulins and serum IgG subclasses, each twin pair had two healthy controls matched for sex and age.

4.   The monozygotic twin material consisted of both concordant and discordant twin pairs, and some unpaired healthy twins.

5.   We therefore separately analysed six discordant twin pairs, and found no significant differences between healthy and affected twins.