Effects of 3,3',5-triiodo-L-thyronine (T3) and dexamethasone (Dex) on the abundance of proteins resolvable by two-dimensional gel electrophoresis were examined in cultured human skin fibroblasts. Confluent cultures were incubated in medium supplemented with thyroidectomized calf serum and were treated with either T3 (100 nM), Dex (100 nM) or both hormones for 2 days and then labelled with [3H]leucine for 1 day. Most of the greater than 100 resolvable radiolabelled proteins were unaffected by hormone treatment. However, both hormones could increase or decrease the abundance of a limited number (approximately 10) of specific proteins. Some of these affected proteins appear to be coregulated. This result is consistent with effects demonstrated previously in pituitary adenoma cultures and suggests that both hormones regulate protein metabolism in human fibroblasts. This may be an ideal model for studying the nature of resistance to thyroid and glucocorticoid hormones.