Generally, the urine samples from the six adult males showed fewer cells and lower amounts of DNA than those from the four adult females, which duplicated the findings of other studies. In the current study, the total DNA concentration of the sequentially sampled urine discharges ranged from 0.02 to 21.3 ng/ml for the males and from 25.0 to 96.9 ng/ml for the females. The estimated midstream DNA yields ranged from 0 to 5 ng/ml for the males and from 4 to 62 ng/ml for females, indicating that urinary DNA concentrations can vary during the course of urination. For comparisons of yields to be relevant, therefore, the collection and sampling methods of the urine specimens must be equivalent, i.e., the part of the urine discharge collected should be specified in reports and publications. Preliminary findings suggest that the ability to recover nuclear DNA from liquid urine samples can be optimized in most cases by collecting the first portion of the urine discharge. Microscopic examination revealed numerous epithelial cells in the sediment samples of most of the females, which probably represented contamination from vaginal and vulvar sources as a result of the collection procedure. Male samples presumably better represented the cellular and DNA of the urinary organs (kidneys, ureters, urinary bladder, and urethra). These are preliminary findings, so additional research is needed in order to evaluate the findings and their implications for forensic casework. All subjects provided two entire urine discharges, first-morning discharges, one as a single specimen and one as a consecutive series of samples. The serial samples were centrifuged, organically extracted, and quantified by slot-blot analysis. 3 tables and 10 references