There has been mounting interest in the use of museum and herbaria collections to assess biodiversity; information is often difficult to locate and access, however, and few recommendations are available for effectively using natural history collections. As part of an effort to inventory vertebrates and vascular plants in U.S. national parks, we searched manually and by computer for specimens originating within or adjacent to 14 parks throughout the northeastern United States. We compared the number of specimens located to collection size to determine whether there was any effect on detection rate of specimens. We evaluated the importance of park characteristics (e.g., age since establishment, size, theme [natural vs. cultural]) for influencing the number of specimens found in a collection. We located >31,000 specimens and compiled associated records (hereafter referred to as specimens) from 78 collections; >9000 specimens were park-significant, originating either within park boundaries or in the local township where the park was located. We found >2000 specimens by means of manual searches, which cost $0.001?0.15 per specimen searched and $0.81?151.95 per specimen found. Collection effort appeared relatively uniform between 1890 and 1980, with low periods corresponding to significant sociopolitical events. Detection rates for specimens were inversely related to collection size. Although specimens were most often located in collections within the region of interest, specimens can be found anywhere, particularly in large collections international in scope, suggesting that global searches will be necessary to evaluate historical biodiversity. Park characteristics indicated that more collecting effort occurred within or adjacent to larger parks established for natural resources than in smaller historical sites. Because many institutions have not yet established electronic databases for collections, manual searches can be useful for retrieving specimens. Our results show that thorough, systematic searching of natural history collections for park-significant specimens can provide a historical perspective on biodiversity for park managers.