The in vitro culture conditions allowing survival and initial proliferation of murine primordial germ cells from 10.5 days post coitum embryos, which include the use of a murine embryonal fibroblast (STO) feeder, were applied to 21 human seminomas, composed of tumour cells which are considered as the malignant counterparts of human primordial germ cells. Cells from 18 seminomas attached poorly to STO, and only a few survived through day 10. In contrast, three seminomas showed a higher degree of attachment. Two of them showed initial proliferation and enhanced survival: 30 days for tumour SE1 and 25 days for tumour SE3. Tumour SE1 was more extensively studied, using the culture conditions allowing the derivation of pluripotent embryonic stem cells from 8.5 days post coitum murine primordial germ cells, which include the use of STO feeder, stem cell factor, leukaemia inhibitory factor and basic fibroblast growth factor. The presence of stem cell factor was necessary and sufficient for colonies of tumour cells to form during the first 3 days of culture. While the cell number decreased after day 3 in medium without fetal calf serum, it increased until day 9 in medium containing fetal calf serum. No reprogramming of SE1 cells to pluripotent stem cells was observed. Our data indicate that seminomas form a tumour population with a heterogeneous in vitro behaviour not equivalent to that of 8.5-10.5 days post coitum murine primordial germ cells.