RB1 and neoplasm: We have previously screened this series of tumours for allelic constitution at chromosome 13 (Bello et al, 1994, and unpublished data) analysing two polymorphic loci (D13S4 and D13S63) as well as the RB1 locus with a cDNA probe used for densitometric analysis on TaqI/MspI Southern blots.