Nested PCR - Contamination problem???? (Aug/28/2003 )

Can anyone tell about nested PCR. I am using it to increase the sensitivity of a PCR, however I am getting a band in my negative control aswell. I have started again with new reagent etc, so I cant see where the contamination is. I get a band in my nested PCR even if I have had no band on my intial 1st round of PCR, however sequencing the nested product shows that the PCR is amplifying the gene I want - but I am very concerned about the negative control being positive.
Has anyone else had a problem like this?

This is certainly caused by contamination and happens most often with nested pcrs. get rid of everything.

You may want to
1. Get rid of everything
2. Wipe everything with 75% alcohol before every run
3. Be sure that pipette tips with air barrier filters are used
4. Spin down reagents before opening the caps
5. Wear clean gloves

Hope it helps.