New DNA typing methods need to be thoroughly validated prior to use in forensic investigations. This includes determining the effects of different sample conditions on the typeability of those samples. Biological samples routinely encountered in forensic case work were exposed to a series of different substrates, environmental conditions, and mixtures and typed for the STR (short tandem repeat) HUMTH01 (Human Tyrosine Hydroxylase, intron 1) using PCR (expansion not provided). None of the conditions resulted in a false typing or preferential allele amplification. In addition to the samples tested for this study, approximately 100 cases (mainly homicides and sexual assaults) were analyzed using HUMTH01 during routine case work investigations in the authors' laboratory. Results of probative value were provided in approximately 95 percent of cases. Positive typings were obtained from such samples as an 11-year-old vaginal swab; a 5-year-old anal swab; a 4-year-old hair sample kept at room temperature; and formalin-fixed-paraffin-embedded fetal tissue, further illustrating the robustness of this system. Tables, references