Objective:To clone human IL-12 cDNA. Methods: IL-12 cDNA (p35 and p40 cDNA) was cloned by RT-PCR from human lymphoblastoid B cell line NC 37, and their sequences were determined by automatic DNA sequencer. Results: There were 2 bases and one base different in p35 sequences of GenBank M 65271 and M 65291 (patent number: 5648467) respectively comparing to our p35 sequence (AF 101062). The third base of 44th code of M 65291 was C, but that of M 65271 or AF 101062 was G. The third base of the 244th code of M 65271 was C, but that of M 65291 or AF 101062 was T. The second base of 247th code was C, but that of M 65291 or AF 101062 was T. In addition, the sequence of our p40 cDNA was identical with that of GenBank (M 38444). Conclusion: Although there are 2 bases and one base different in p35 cDNA sequence of Genbank M 65271 and M 65291 respectively, comparing to AF 101062, the sequence of corresponding amino acids of AF 101062 is identical with that patented one. The recombinant IL-12 expressed by our p35 and p40 cDNA is acceptable in theory.