Various strains of laboratory-bred rodents viz. mice [Swiss, C57BL/6, C3H/Hej, DBA/2, BALB/c, NMRI (nu/nu) and BL6 (nu/nu) and their heterozygous siblings (nu/+)], Mastomys natalensis, Wistar rat, golden hamster and Indian desert gerbil were inoculated intracerebrally (ic) with mouse-adapted dengue virus type 2 (DV-2). The inoculated animals were observed daily for dullness, anorexia, occult blood in faeces, patechial haemorrhages, lacrymation, paralysis, cachexia, death. Necropsied animals were examined for gastrointestinal haemorrhages and lymphadenopathy. The severity of clinical symptoms in various rodents declined as follows: (i) BL6 (nu/nu) mice exhibited most severe manifestation of all the aforementioned symptoms followed by (ii) NMRI (nu/nu), (iii) BL6 (nu/+) (iv) NMRI (nu/+) and C57BL6, (v) DBA, C3H/Hej and BALB/c, and (vi) Swiss. These results indicate that adaptation of DV-2 to the mouse may be an important factor in exaltation of virulence. Interstrain variation in manifestation of symptoms in mice indicates that the susceptibility to DV-2 may be determined by host genetic factors.