Accurate blood group antigen typing of red blood cells with a positive direct antiglobulin test or from a recently transfused patient has been a long-standing problem. To overcome this problem, we evaluated the feasibility of using somatic cells as a source of DNA for molecular genotyping. Two sources of cells that could be obtained by noninvasive procedures were chosen for analysis: urine samples, which were already available in the clinical laboratory, and buccal epithelial cells collected with cotton wool swabs. DNA, prepared using a commercial kit, was subjected to polymerase chain reaction amplification and followed by digestion with the appropriate restriction enzyme. Genotyping was performed for three alleles encoded by polymorphic genes on three different chromosomes, namely KEL1/KEL2, JKA/JKB, and FYA/FYB. Genotyping results were compared to the results of typing performed on red blood cells using standard hemagglutination techniques. Results given by samples freshly collected from volunteer donors were concordant. Although results obtained with samples collected from hospital patients were initially not in agreement with the phenotyping results, adjustments to the test protocol resulted in concordance. DNA from blood, urine sediment, or buccal cells can be used for blood group molecular genotyping.