Clinical and microbiologic measures of oral health were assessed in all crew members of each Skylab mission. Clinical factors included preflight and postflight clinical services, provisions for in-flight emergency dental care, and the preflight and postflight monitoring of alterations in clinical indexes of oral health. Microbiologic measures included the preflight and postflight monitoring of changes in microbial populations at various intraoral sites. Problems involving preflight and postflight clinical services were minimal and easily resolved. In-flight dental problems requiring emergency self-treatment were not encountered. Moderate increases were observed in the in-flight increments of dental plaque, calcalus, and gingival inflammation. With the possible exception of gingival inflammation, mission-related changes in clinical indexes of oral health mainly corresponded to those of comparable periods under more conventional circumstances. Microbiologic assessments showed noteworthy elevations in counts of specific anaerobic components of the oral microflora, streptococci, neisseria, lactobacilli, and enteric bacilli. Since most microbial changes occurred after the preflight incorporation of the space diet, they were believed to be diet related. The most meaningful finding of the study was the relative absence of intraoral changes that are hazardous to one's health.