An extensive Newfoundland genealogy shows a large number of cases of lymphoreticular malignancies. A recessive pattern of inheritance had been previously suggested, but no quantitative investigation of the hypothesis was made. Here we have investigated a variety of aspects of the descent structure of the pedigree and shown that for only a subset of the traits can the inference be upheld. For Hodgkin's disease (HD) and generalized immunodeficiency (ID) there is clear evidence for a recessive HD/ID susceptibility allele. The remainder do not follow this pattern, show no evidence of a single-locus effect and little of any genetic effect. The ancestry of the HD/ID cases was therefore investigated in detail, and likelihoods computed on the pedigree. These confirmed the recessive nature of the trait, as also did the risk analysis which quite clearly identified the paths of descent taken by the allele. The determination of these paths is a prerequisite for any linkage analysis which might further confirm the single-locus nature of the trait.