The human body is composed of diverse cell types with distinct functions. 
Although it is known that lineage specification depends on cell-specific gene 
expression, which in turn is driven by promoters, enhancers, insulators and 
other cis-regulatory DNA sequences for each gene, the relative roles of these 
regulatory elements in this process are not clear. We have previously developed 
a chromatin-immunoprecipitation-based microarray method (ChIP-chip) to locate 
promoters, enhancers and insulators in the human genome. Here we use the same 
approach to identify these elements in multiple cell types and investigate their 
roles in cell-type-specific gene expression. We observed that the chromatin 
state at promoters and CTCF-binding at insulators is largely invariant across 
diverse cell types. In contrast, enhancers are marked with highly 
cell-type-specific histone modification patterns, strongly correlate to 
cell-type-specific gene expression programs on a global scale, and are 
functionally active in a cell-type-specific manner. Our results define over 
55,000 potential transcriptional enhancers in the human genome, significantly 
expanding the current catalogue of human enhancers and highlighting the role of 
these elements in cell-type-specific gene expression.