Predominantly neuronal (neuronal) or non-neuronal (glial) cerebral cortical cell cultures were employed to study the kinetics and changes with maturation of125I-diferric-transferrin uptake. The diferric-transferrin association curve of neuronal cultures at 37°C was nonphasic and indicated equilibrium at 90 minutes. Dissociation was completed by 70 minutes. Diferric-transferrin specific uptake (80% of total) in neuronal cells (evaluated at days 6, 9, 13, 16, and 23 in culture) increased with maturation. Scatchard transformation of the data revealed increasing Bmax from day 6 to day 16 in culture (1626 to 2740 fmoles/mg protein). However, the Kuptake was statistically unchanged over time and equaled 48.7±13.9 nM (mean ±SD). In contrast, association studies of glial cultures documented equilibrium by 45 minutes and dissociation by 40 minutes. The concentration curves for differric-transferrin uptake in glial cells, evaluated at days 11, 15, and 18 in culture, revealed virtually identical uptake at the three ages studied, but the percent specific uptake (58%) was less than for neurons (88%). Scatchard transformation of the data revealed no statistical alteration of Bmax or Kuptake from days 11 to 18 in culture. Bmax ranged from 595 to 751 fmol/mg protein; overall Kuptake was 48.3±13.2 nM (mean±SD).