The composition of human beta-crystallins displayed specific changes with age and region of the lens. 27kD and 29kD human beta-crystallin subunits were singled out for study. The 29kD beta-crystallin subunit constituted approximately 10% of the total lens crystallins at 8 months of fetal life. Its accumulation decreased steadily to 3.3% during postnatal year 1, to 0.5% by year 5 and to 0.3% thereafter. At all postnatal ages, however, it persisted mainly in the superficial fibers. Thus in a 17-years old lens it made up 1.3% of the superficial fiber soluble protein but was already absent from deep cortical and nuclear fibers. The 27kD subunit increased steadily from 3.5% at 8 months fetal to 7% at year 5; it then decreased steadily to 1.2% in the 86-years old lens. It persisted in all regions of the lens but decreased markedly in the deep cortical and nuclear fibers with increasing age beginning at 5–17 years of age. Studies on the oligomeric structure of human beta-crystallin must take into account age-related changing quantitative patterns in the subunit polypeptide composition of this lens protein.