Small cell lung cancer (SCLC) is a very malignant tumor known to grow aggressively and to metastasize early. It is well established that metastasis generally involves both tumor cell adhesion and proteolytic degradation of the extracellular matrix. However, SCLC cells cultured in vitro, such as the classic SCLC cell line NCI-H69, grow in floating aggregates and express only negligible proteolytic activity. In this report, we show that NCI-H69 cells can be selected for adherent growth. In contrast to parental suspension cells, the adherent cells were found to express tissue factor as well as gelatinolytic activity, attributable to matrix metalloproteinases 2 and 9. Such a switch of tumor cell characteristics, if it could occur in SCLC patients, might add to the understanding of the steps involved in the spreading of this highly metastatic type of lung cancer.