A new cell line, GS, of human renal cell carcinoma was established and characterized. It was derived from a metastasis of a human renal cell carcinoma, which appeared 6 years after nephrectomy. The GS cells exhibit basic characteristics of renal cell carcinoma: epithelial cell character, PAS and glycogen positivity, typical ultrastructural features. The cells have a pseudotriploid stemline with a modal number of 75 chromosomes and two marker chromosomes. GS cells formed neither colonies in soft agar nor transplantable tumours in nude mice but produced a factor(s) stimulating growth and colony forming activity of indicator cells.