this work aimed at verifying the influence of propilthiouracil (ptu)-induced thyroid hormone deficiency on gingival mucosa of young male rats, measuring total protein concentration, collagen content and dna concentration as indices of cellular population. fifty sprague-dawley rats were used. the animals were grouped in: ptu-treated (i.p. 10 mg/d) and control rats (c). the experience was maintained for a period of 10 weeks. total protein content of gingival mucosa tissue was determined by the lowry method; hydroxyprolin rate, as prototype aminoacid of collagen, was determined using the newman method, and dna concentration was measured by burton's methodology. the results showed decreased amounts of ptu-treated rats gingival total protein content (ptu= 41.23 ± 24.05 vs. c= 63.36 ± 18.05); no alterations were seen in hydroxyprolin concentration neither in dna content of ptu treated rats, respectively (ptu= 2.18 ± 1.48 vs. c= 2.29 ± 1.51) and (ptu= 0.33 ± 0.19 vs. c= 0.46 ± 0.41). thus, ptu treatment promotes a decrease in total protein content of rat gingival mucosa that may be interpreted as a decrease in protein synthesis induced by the hypothyroid condition, but with no alteration either in collagen or nucleic acid rates.