The technique of labelled mitoses and flow cytometric DNA analysis were used to determine the proliferation kinetics of a human malignant melanoma grown in nude mice. The effect of tumour volume and of long-term serial transplantation on the kinetic parameters was investigated. The results showed that the cell loss factor, which was the dominant factor in the growth of this melanoma, increased from 52 to 69% with increasing tumour size, whereas the calculated growth fraction showed no systematic changes. The cell generation time increased from 34 to 44 hr with tumour size, mainly due to a prolongation of the G1 duration time, whereas no significant changes occurred in the duration of the S and G2 phases of the cell cycle. The stability of the investigated tumour characteristics indicated that the kinetics of this melanoma remained unchanged during more than sixty serial transplantations in nude mice. The methods applied are suitable for a detailed description of tumour growth kinetics, since they provide complementary results.