To separate the connective tissue cells expressing the 43-kDa zinc-binding protein from the common carp, mucosa of the digestive tract of the fish was removed by scraping with a glass slide, and the de-mucosa tissue was digested with a collagenase type IV solution. The cells collected from the collagenase-treated suspension were rather homogeneous, and more than 90% of the cells were round with a diameter of approximately 6 mm. Significant quantities of the 43 kDa zinc-binding protein were shown to be present on the cell surface of the approximately 6-mm cells. The mean zinc concentration in the cells was found to be 2.21 mg zinc/10 6 cells, which is approximately 20-30 times higher than that found in the other three fish species (grass carp, silver carp, tilapia) studied. The present work may provide a basis for the culture of these cells.