Premolar and third molar dental pulps were studied. The amount of collagen in the dried pulps was 25.7 per cent in premolars and 31.9 per cent in third molars. These percentages are much higher than those reported for pulps in other species. Significant differences were further found in the collagen content and cell distribution (DNA) of the coronal, middle and apical parts of the pulp. Collagen content was the lowest in the coronal part, while the cell content was the lowest in the middle part. The extractability of collagen in a neutral salt solution or 0.5 M acetic acid was found to be extremely low (less than 1 per cent). Pretreatment of the pulp with hyaluronidase in order to remove proteoglycans had no effect on the solubility. It is concluded that human pulp collagen is highly cross-linked and cannot be considered as immature. Characterization of collagen was performed by methods in which limited pepsin digestion or CNBr cleavage was used. The digests were analysed by means of quantitative electrophoresis which revealed an amount of 42.6 per cent type III of the total collagen. Because of the large differences between dental pulps from man and experimental animals, extreme caution should be exercised in drawing conclusions from data of other species to explain phenomena observed in human teeth.