Automated DNA sequencers draw the four-base profiles of a sample with four different colors, but it is also possible to draw the profiles of a base-specific reaction of four different samples with four colors. PCR-amplified DNAs from four individuals were subjected to a single base-specific sequencing reaction and the products were applied to a set of four lanes of an automated DNA sequencer. A base substitution in an individual was clearly identified as an individual-specific peak with a color specific for the individual. In this way, we analyzed more than 50 individuals and identified several polymorphic base substitutions. The sensitivity of this method was high enough to allow detection of the mutation/polymorphism even if samples from several individuals were applied to one lane. Thus, our method is applicable to screening of a large number of samples in an automated manner.