Previous studies showed that the tendency to develop gingivitis differed between pre-school children with deciduous dentition and adults. A similar difference was noted between juvenile dogs with deciduous teeth and adult dogs with permanent teeth. The juvenile dogs showed morphologic characteristics which might interfere with the permeability of the junctional epithelium, thus protecting the underlying tissues from bacterial irritation. An indirect way to test whether structural differences of clinical importance exist in humans between the gingiva at deciduous and that at permanent teeth is to study the gingival reaction to a controlled amount of plaque in children with mixed dentition. The present paper reports an intra-individual comparison of the gingival reaction at deciduous teeth with that at permanent teeth. 30 children, 7-9 years of age, took part in the study. The amount of plaque was assessed in terms of the plaque index and the degree of gingival inflammation by applying the gingival index. The mean distribution of gingival index scores did not differ significantly between deciduous and permanent teeth, but a higher % of plaque index score 2 + 3 was found in permanent teeth. In the comparison based on areas of similar plaque irritation, a tendency toward a higher degree of gingivitis was found at the deciduous teeth. The results indicate that structural differences, if any, between the gingiva at deciduous teeth and that at permanent teeth have no impact of clinical significance on the gingivitis reaction.