In this study, we analyzed the expression of messenger (m)RNAs for laminin B1 chain, alpha 1 (IV) chain of type IV collagen, and 72-kd type IV collagenase in 15 primary lung carcinomas and in two metastatic adenocarcinomas to the lung. The results show that the mRNA synthesis for these proteins mainly occurs in the stromal fibroblasts and endothelial cells. In a proportion of tumors, mRNAs for laminin B1 chain and 72-kd type IV collagenase could also be observed in carcinoma cells, but the amount of mRNAs was considerably lower in them than in the stromal cells. There were no convincing signals for the presence of the alpha 1 (IV) chain of type IV collagen mRNA in any of the carcinoma cells. A simultaneous expression or lack of expression of signals for laminin B1 chain and 72-kd type IV collagenase mRNAs could be observed in carcinoma cells of 12 cases, suggesting that the activation of these two genes may be somehow connected. There was no association between the mRNA expression and the differentiation degree or the size of the tumors. The occurrence of the mRNA synthesis for the 72-kd type IV collagenase in stromal fibroblasts and endothelial cells indicates that the stromal cells of tumors have a more pronounced impact on the spread of the neoplastic disease than previously thought. The results further show that in their ability to synthesize these proteins the stromal cells of tumors resemble those of developing embryonic tissues. This resemblance is probably connected with the constant remodeling of extracellular matrix in response to the proliferative activity of carcinoma cells.