It has been found possible to detect the presence of some gamma chain abnormal fetal hemoglobins in adults through analysis of genomic DNA with selected restriction endonucleases. These variants are Hb F-Hull (A gamma 121Glu----Lys) which was observed in eight adult members of five families, Hb F-Pendergrass (A gamma 36Pro----Arg) in five adult members of one family, and Hb F-Port Royal (G gamma 125Glu----Ala) in 32 adult members of 17 families. The analyses were extended to include haplotyping, which involved 12 different restriction sites. The Hb F- Port Royal anomaly was only present on a chromosome with two G gamma genes (the 5′-G gamma-G gamma-3′ globin gene arrangement) which may have arisen through gene conversion or point mutations. It appears likely that the mutation resulting in the 125Glu----Ala substitution occurred once on a 5′-G gamma-G gamma-3′ chromosome, while additional base substitutions, gene conversions, and/or cross-over events are responsible for the association of the F-Port Royal anomaly with different chromosomes, as characterized by different haplotypes.