AbstractThree preparations of recombinant basic fibroblast growth factor (bFGF, FGF-2) were evaluated, using a variety ofin vitrobioassays and immunoassays, by 11 laboratories in six countries for their suitability to serve as international standards (IS) for bFGF. Two preparations of human sequence bFGF showed broadly similar behavior in different assays, but the relative activity of the third preparation, a modification of the human sequence, showed more variability. All three preparations were predicted to be sufficiently stable to serve as an IS. On the basis of the results reported here, the World Health Organization (WHO) established one of the preparations (coded 90/712) as the international standard for basic fibroblast growth factor, and assigned it a content of 1600 International Units (IU) per ampoule. The IS may be obtained for use in the calibration of local standards by writing to NIBSC, PO Box 1193, Potters Bar, EN6 3QH, UK.