We describe a rapid and reliable micromethod for DNA isolation from buccal epithelial cells from the interior mouth mucosa. This convenient, noninvasive method could be applied to genetic typing in a small number of cells (about 2000 cells per cheek). We have shown that DNA released by this method is suitable for further amplification by polymerase chain reaction (PCR). Using this protocol, coupled with the PCR-RFLP (restriction fragment length polymorphism) method, we analyzed the allelic sequence diversity of the human lymphocyte antigen (HLA) class II genes in an extended family of 33 persons containing 14 asthmatic or atopic members. Six of eight DQA1 alleles, and 11 DQB1, 20 DPB1, and 10 DR haplotypes could be identified in a single DNA sample. Our results suggest that the DR53 group haplotype is frequently associated with allergic asthma and atopy. The micromethod described here may be useful in genetic epidemiology, especially in family studies involving small children.