Nonsyndromic cleft lip with or without cleft palate is a common birth defect, affecting approximately 1 in 1,000 Caucasian newborns. Thirty-five multiplex families from the mid-Atlantic region of the United States and 22 families from central Mexico with a nonsyndromic form of cleft lip with or without cleft palate were selected for a linkage analysis. A tetranucleotide repeat marker (D2S443) located on the same yeast artificial chromosome as the transforming growth factor alpha locus was tested for linkage to a putative susceptibility Mendelian locus under varying levels of pentrance. No evidence for linkage between D2S443 and a susceptibility locus for cleft lip with or without cleft palate was found. Insight is given to explain this outcome in spite of the statistically significant associations found by other investigators.