NMR spectroscopic and statistical methods have been applied to investigate the 
biochemical variations within and between two phenotypically normal rat strains. 
The 600 MHz (1)H NMR spectra of urine were acquired as part of a series of drug 
toxicity studies from 450 control rat urine samples from each of two strains of 
laboratory rat (Han Wistar and Sprague Dawley). The spectra were data-reduced to 
256 intensity descriptors over a range of delta 0.2-10.0. The spectral variation 
was analysed both within and between strains in terms of the mean, standard 
deviation, skewness and kurtosis of each descriptor. It is demonstrated that 
spectral intensities corresponding to a number of endogenous metabolites do not 
show Gaussian distributions and there is evidence for bimodality for some 
metabolites. Additionally, despite the visual similarity of the NMR spectra from 
the two strains of rat, the descriptor distributions and the statistics derived 
from them revealed differences in the metabolite profiles, which clearly 
distinguished the two populations. This work is of value in the determination of 
biochemical normality and variability, and thus can be used to investigate, and 
place confidence limits on the biochemical deviations, which arise as a 
consequence of genetic modification or pathophysiological events.