PCR problem - (Sep/05/2013 )

Hi,

When I use above 15 DNA samples, my PCR doesn' t work but when I use below 15 (same DNA), the pcr is perfect. I use invitrogen' s taq dna polymerase, dntp. According to you what is the problem?

some more details would be good. Are you using a mastermix?

Yes, I use mm everytime.