The nymph and larva of Haemaphysalis (Rhiplistoma) asiatica (Supino) are described and and confirmed as this species by reared adult specimens and their immature stage exuviae, and by other nymphs and larvae from the same collections from forested areas of southcentral Thailand. Immature stages infested tree shrews, Tupaia glis subsp., Berdmore squirrels, Menetes berdmorei subsp., and rats, Rattus sp., and were also collected from forest vegetation. Nymphs and larvae previously tentatively identified as H. (R.) asiatica (sic asiaticus) belong to a different species. Field-collected tick nymphs and larvae from Borneo were tentatively attributed to Haemaphysalis (Rhipistoma) asiatica (Supino) (Hoogstraal and Trapido, 1966). Subsequent study of immature ticks and of exuviae of immature ticks reared to adult H. (R.) asiatica in Thailand shows that the Borneo sample is a different species which cannot be associated with adults until reared material is available for comparison. The immature stages of H. (R.) asiatica are described and confirmed by reared adult specimens, larvae and nymphs, and exuviae. Collection data and laboratory observations are included. This experience points to the need for rearing field-collected larvae and nymphs to the following developmental stage to associate immature and adult stages of poorly known tick species. Many small wild vertebrate animals are easily held alive till ticks detach (Kaiser and HoogReceived for publication 18 May 1971. * From Research Project MF12.524.009-3010, Bureau of Medicine and Surgery, Department of the Navy, Washington, D. C. The opinions and assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views of the Department of the Navy or of the naval service at large. The illustrations in this report were prepared under the auspices of Agreement 03-005-01 between the NIAID (NIH) and NAMRU-3. t Medical Zoology Department, Niigata University School of Medicine, Niigata City, Japan. t Medical Zoology Department, U. S. Naval Medical Research Unit Number Three (NAMRU-3), c/o Spanish Embassy, Cairo, Egypt, UAR. ? Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand. straal, 1968). Epidemiological and diseasetransmission studies often require field collecti n of small vertebrate hosts infested by larval and nymphal ticks. Owing to the frequent difficulty or impossibility of identifying immature tick stages, much critical data may be lost if these parasites are not held until they molt to adults (Hoogstraal and Kaiser, 1960). As in the initial period of Kyasanur Forest disease research, once the tick fauna of an area is learned and immature and adult stages are associated, keys to each stage can be prepared and rearing is no, longer necessary for identification (Hoogstraal, 1966; Trapido et al., 1964). Recently Dr. Vladimir Cerny of Prague has called our attention (pers. corresp. with H.H.) to the fact that asiaticus should be corrected to asiatica since the generic name Haemaphysalis is feminine. Haemaphysalis (Rhipistoma) asiatica (Supino) Southeast Asian grooved haemaphysalid (Figs. 1-15)