Improvements in genetic mapping techniques have driven recent progress in human genetics. The use of single nucleotide polymorphisms (SNPs) as biallelic genetic markers offers the promise of rapid, highly automated genotyping. As maps of SNPs and the techniques for genotyping them are being developed, it is important to consider what properties such maps must have in order for them to be useful for linkage studies. I examine how polymorphic and densely spaced biallelic markers need to be for extraction of most of the inheritance information from human pedigrees, and compare maps of biallelics with today's genome-scanning sets of microsatellite markers. I conclude that a map of 700-900 moderately polymorphic biallelic markers is equivalent--and a map of 1,500-3,000 superior--to the current 300-400 microsatellite marker sets.