Over the past decade new technologies have been developed to elucidate ways in which cells acclimate to environmental change. Many of these techniques have allowed the identification of specific transcripts that change in abundance in response to particular environmental stimuli; such transcripts represent genes that are potentially differentially regulated. Two techniques that foster identification of differentially regulated genes are differential display and expression profiling using high density DNA microarrays. The former technology amplifies cDNA fragments from mRNAs that differentially accumulate under specific environmental conditions, while the latter provides a more global view of changes in gene expression in response to environmental stimuli. Coupling these technologies with the analysis of mutants aberrant for regulatory molecules that participate in acclimation processes will allow the identification of groups of genes controlled by specific regulatory elements. In this article we describe the use of differential display and DNA microarray profiling to examine environmentally-regulated gene expression. We also show specific experiments using the unicellular green alga Chlamydomonas reinhardtii, in which mRNA abundance is evaluated in response to both changing light and CO(2) conditions.