IGH rearrangement analysis of case no. 18 by Southern blotting. DNA was digested with BamHI restriction enzyme and the same filter was subsequently hybridized with the JH and C1 probe. Comigrating JH- and C-rearranged fragments are indicated by an arrowhead; germ line bands (approximately 18 kb in length) are indicated by a dash. The asterisk shows a JH cross-hybridizing band of approximately 10 kb detectable under our experimental conditions.