Termites (Isoptera) are separated into morphologically and behaviorally distinct eusocial castes. We hypothesized that the differences between castes are due to differences in gene expression levels. We are presenting the general gene ontology (GO) proportions between 17,000 expressed sequence tags (ESTs) of three caste (workers, soldiers, and alates) specific cDNA libraries of the termite Reticulitermes flavipes. Putative gene function was assigned using a BLAST similarity search. The libraries had about 70-90% of sequences with no significant homology to other sequences (e-value<1E-10). ESTs of workers and soldiers were from the widest array of classes and workers had the highest diversity of putative sequences from insect orders. All libraries showed sequences with putative functions assigned to reproduction, which is unexpected in both the soldier and worker libraries. The biological process ontology was most variable for the worker caste with three unique terms (reproductive process, biological adhesion, and growth), however soldiers did have 10% of the ontology terms represented as sequences that made up less than 1% of the total, while workers consisted of 8% indicating increased functional variability in the soldier ESTs. We plan on undertaking further GO analysis on two larval life stages and utilizing these data to conduct expression studies using a microarray. This comparative analysis provides us with an initial estimate of possible gene expression differences within the individual castes and life stages.