Using 5′- primers corresponding to leader sequence,3′- primers to constant region,and conventional PCR protocol,only 4 out of 10 variable region cDNAs of the 5 monoclonal antibodies were amplified.A novel protocol was designed and tested which included one more time phase of reaction:94℃ 1 min,37℃ 6-8min,1-3 cycles,with 5′-primer but no 3′-primer.Conventional PCR cvcles started after 3′- primer was supplemented.As a result,all 10 variable region cDNAs were successfully amplified.This novel protocol was named “single primer preincorporation PCR”.