We determined the nucleotide sequence of a 2.5 kb DNA fragment (1 kb is 10(3) base-pairs) that includes exon 1, intron 1 and about 1.4 kb of 5'-flanking DNA of the spider monkey gamma 1-globin pseudogene locus and compared this sequence to its homologous from other primates and rabbit. This region of the gamma 1 locus of spider monkey still retains conserved regulatory elements, suggesting that it became a pseudogene late in New World monkey phylogeny. In the 250 base-pair region immediately 5' from the transcription start site where many known regulatory elements are located, a higher rate of nucleotide substitutions occurred in the ancestral anthropoid (human, ape and monkey) lineage than in the prosimian (galago) lineage, as was also the case for non-synonymous substitutions in the coding region. The opposite pattern was observed for most other non-coding regions and for synonymous substitutions. These substitution patterns correlate with the embryonic-to-fetal transformation of the gamma-globin genes of the ancestral anthropoids. Analysis of the 5'-flanking sequences suggests that 11 gene conversion events have occurred in the anthropoid gamma-gene lineages. In the parts of the 5'-flanking region where no gene conversions have been detected, gamma 2-gene sequences have accumulated more nucleotide changes than gamma 1, which suggests that the gamma 2 gene was the more redundant duplicate that may have accumulated first the nucleotide changes responsible for the anthropoid fetal pattern of gamma-globin gene expression.