We conducted studies to determine the minimum primer length required for PCR amplification by the S-Tbr and Taq polymerases. For initial testing, primers were designed based on the nondegenerate versions of the 27F (sometimes called 8F) and 1492R primers used to amplify bacterial 16S rRNA genes (designated 27F-P and 1492R-P in this work) (Table (Table1)1) (18). Beginning with a 20-nt forward primer sequence (Fig. (Fig.1A),1A), we designed a series of progressively shorter primers with lengths from 20 to 8 nt (Fig. (Fig.1A).1A). To determine the lower limit for primer length, PCRs were performed using a forward primer from the series of decreasing lengths paired with a 19-nt reverse primer; E. coli genomic DNA was used as the template (Fig. (Fig.1B).1B). With S-Tbr polymerase, successful amplification resulted with a primer as short as 10 nt. In a parallel experiment, Taq required the primer to be longer than 14 nt for detectable amplification (Fig. (Fig.1B).1B). PCR products were produced with forward and reverse primers of 10 nt at annealing temperatures as high as ∼49°C (Fig. (Fig.1C).1C). To distinguish this new PCR method from traditional Taq PCR, we refer to the shortened primers as “miniprimers” and to PCR using them as “miniprimer PCR”.