The STR loci were HUMCD4, HUMTH01, HUMTPOX, and HUMCSF1P0. After a multiplex polymerase chain reaction (PCR)-amplification, semiautomatic DNA profiling was performed by using an Automated Laser Fluorescent A.L.F.express DNA Sequencer. Conditions were optimized for the PCR co-amplification of the four STR loci, and the quadruplex PCR was performed on various forensic DNA samples, such as whole blood, bloodstains, teeth, and saliva from Caucasians living in Northeast Italy. The distribution of the genotype frequencies showed no significant deviation from Hardy-Weinberg expectations in the sampled population. The combined power of discrimination of the quadruplex was 0.9999. Thus, the Northeast Italian population allele frequency data for the selected four STR loci do not differ substantially from other Caucasian data for the same loci. The quadruplex PCR amplification of the four loci is easy to perform and gives a good amplification signal with small amounts of DNA template when using a monochrome automated laser fluorescence sequencer. The efficiency, precision, and high degree of discrimination of this quadruplex STR system suggests its possible application in numerous routine forensic analyses for human identification and paternity testing in forensic sciences. 1 figure, 2 tables, and 16 references