The use of antibodies to visualize the distribution and subcellular localization of gene products powerfully complements genetic and molecular analysis of gene function in C. elegans. The challenge to immunolabeling C. elegans is finding the fixation and permeabilization methods that effectively make antigens accessible without destroying the tissue morphology or the antigen. Embryos are surrounded by a chitinous eggshell and larvae and adults are surrounded by a collagenous cuticle, each of which must be permeabilized to allow penetration of antibodies. In addition, antigens and antibodies are sensitive to different fixing and permeabilizing conditions. For example, some antibodies do not work well on paraformaldehydefixed samples, and others are sensitive to incubation in acetone. There are many protocols used in the C. elegans field; additional protocols are summarized in Miller and Shakes (1994) and on the C. elegans World Wide Web page
(http://elegans.swmed.edu/).