Haplotypes, combinations of several phase-determined polymorphic markers, are extremely valuable for studies of disease association and chromosome evolution. Here we describe a technique called M1-PCR (M for "multiplex" and 1 for "single-copy DNA molecules") that enables direct molecular haplotyping of several polymorphic markers separated by as many as 24 kb. A genomic DNA sample first is diluted to approximately single-copy. The haplotype is directly determined by simultaneously genotyping several polymorphic markers in the same reaction with a multiplex PCR and base extension reaction. This approach does not rely on pedigree data and does not require previous amplification of the entire genomic region containing the selected markers.