Abstract. Much of the basic clinical information about dengue infection comes from experimental human studies conducted in the 1920s and 1940s. Albert Sabin's original laboratory records from one such study were bequeathed to Duane J. Gubler. These records were reviewed and 150 experiments were included in our analyses. Persons were inoculated with dengue virus 1 (DENV-1) and DENV-2. Median fever duration was shorter in primary DENV-2 infections compared with DENV-1, although maximum temperature and severity of illness were comparable. At 1.5-9 months after primary infection, 20 persons were inoculated with the heterologous serotype. Only one person inoculated with a heterologous serotype at 8 weeks showed development of a clinical infection with a maximum temperature of 38 C, and 7 (88%) of 8 persons inoculated with a heterologous serotype at 4-9 months post-primary infection showed development of fever. On average, persons had a shorter incubation period in secondary infection compared with primary infection.