Three statistical/mathematical analyses are carried out on isochore sequences: 
spectral analysis, analysis of variance, and segmentation analysis. Spectral 
analysis shows that there are GC content fluctuations at different length scales 
in isochore sequences. The analysis of variance shows that the null hypothesis 
(the mean value of a group of GC contents remains the same along the sequence) 
may or may not be rejected for an isochore sequence, depending on the subwindow 
sizes at which GC contents are sampled, and the window size within which group 
members are defined. The segmentation analysis shows that there are stronger 
indications of GC content changes at isochore borders than within an isochore. 
These analyses support the notion of isochore sequences, but reject the 
assumption that isochore sequences are homogeneous at the base level. An 
isochore sequence may pass a homogeneity test when GC content fluctuations at 
smaller length scales are ignored or averaged out.