The von Recklinghausen neurofibromatosis (NF1) gene has been localized to the pericentromeric region of chromosome 17. We have screened six multigenerational families with multiple, tightly linked markers to aid in mapping this region of the chromosome. More than 150 members in six families were typed with probes including HHH202, D17Z1, EW203, EW206, EW207, EW301, pA10-41, D17S37, and D17S36. Two-point lod scores for NF1 versus all markers were calculated. HHH202 demonstrated the tightest linkage to NF1 with theta = .0, z = 3.86 (95% confidence limits [CL] of theta = .0-.13), suggesting that HHH202 be considered as a potential candidate marker for use in carrier detection and prenatal diagnosis. Pairwise marker-to-marker lod scores were used in examining the most likely order of subsets of the markers. Of those tested, the most likely order was (pter)-pA10-41-EW301-D17Z1-HHH202-NF1-E W206-EW207-EW203-(qter). In addition, we have ascertained an NF1 x NF1 half-cousin mating in which there are four affected family members who are potentially homozygous for the disease gene. Two of these four individuals have been sampled and typed for marker loci. When their D17Z1 genotypes are considered, the probability that both these individuals are heterozygous is 85%.