IgM- and IgG-capture ELISAs are widely used as diagnostic tests for confirmation of dengue virus infection. The positive rate of anti-dengue IgM and IgG detection was examined in primary and secondary dengue virus infections in the setting of a provincial hospital using IgM- and IgG-capture ELISAs. Disease day 1 was defined as the day of onset of symptoms. In total, 232 plasma samples were collected from 106 confirmed dengue cases consisting of 12 primary and 94 secondary infections. In primary infection, anti-dengue IgM was detected in 4 out of 5 samples collected on disease day 5 and in all the 21 samples collected on disease day 6 or later. Specific IgG was detected in 2 out of 5 samples collected on day 12, and in 5 out of 6 samples collected on disease days 13-15, but was not detected in samples collected on disease day 10 or earlier. In secondary infection, IgM was not detected in the samples on disease days 2 and 3, but detected in 20 out of 79 samples collected on days 4-6, in 44 out of 65 on disease days 7-11 and in 40 out of 51 samples on disease days 12-14. In contrast, specific IgG was detected in 21 out of 60 samples on disease days 4 and 5, in 13 out of 19 on disease day 6, in 62 out of 65 on disease days 7-11 and in all the samples collected on disease day 12 or later. The result indicate that seroconversion rates of IgM and IgG are different between primary and secondary infections, and suggest that detection of specific IgM and IgG is necessary for determining dengue virus infection and for differentiating primary and secondary dengue infections.