Antigen levels of t-PA were determined in 24h-conditioned medium of five human primary cell types (endothelial cells, astrocytes, fibroblasts, monocytes and hepatocytes) and six human transformed cell lines (Bowes melanoma cells; HT1080 fibrosarcoma cells, HeLa cells, HepG2 and Huh7 hepatoma cells, and NB4 acute promyelocytic leukemia cells). Here, PLAT is linked to acute promyelocytic leukemia.