H. J. Conn of the New York Agricultural Experiment Station was the founder and leader of the Commission on the Standardization of Biological Stains. This Commission ultimately evolved into the present Biological Stain Commission. Conn did much to determine the chemistry of stains and to promote their applications in biology. Interestingly, Conn was a microbiologist and co-authored an early textbook entitled `` Bacteriology ’’ (Williams and Wilkins, 1st ed., 1923). It was ® tting for the Biological Stain Commission, at its 79th annual meeting, to convene a scienti® c session devoted to microbiological stains and stains employed in contemporary molecular biology. The most important stain in microbiology is the Gram stain. The mechanism of this empirical stain remained unresolved until Terry Beveridge and his colleagues (University of Guelph) developed seminal techniques to show that the Gram-positive character was due to physical entrapment of the dye. During the 1980s, Beveridge et al. published the de® nitive work on the Gram stain mechanism. In the scienti® c session, Dr Beveridge reviewed the history of the Gram stain and provided a critical description of its mechanism. During the past several decades important new stains have been discovered that proved to have signi® cant use in the clinical diagnostic microbiology laboratory. Dyes are available that speci® cally stain capsules, ¯ agella, spores, nucleic acids, polyphosphates, polysaccharides, lipids and proteins. Dr Berneice Madison (Centers for Disease Control, Atlanta) described the most commonly employed stains in diagnostic microbiology. She not only provided a lucid discussion of the general properties of the stains, but gave speci® c applications and de® ned their limits and reliabilities as well. During the past three decades, molecular biology has emerged as an essential component of all aspects of biology and medicine. Molecular biology assumed its elevated position partially because techniques were developed for electrophoresis and blotting. These techniques required the use of new and sensitive stains to detect minute amounts of protein and/or nucleic acids. Dr Lisa Williams (University of Louisville) gave an elegant overview of most of the stains utilized to detect molecules on gels and blots. Her presentation not only provided a background on the mechanisms of the individual dyes and stains, but also included examples of their use. Science is incremental. The genius of Conn and others early in the 20th century is now paying large dividends for scientists in the 21st century.