Sodium antimony gluconate (SAG) is the mainstay of treatment for visceral leishmaniasis (VL) or kala-azar. In view of the increasing incidence of refractoriness to SAG in India, we compared the levels of parasite-specific IgG and IgG subclasses in 20 longitudinally followed up kala-azar patients. In both SAG-responsive (n = 10) and unresponsive patients (n = 10), the levels of total IgG, IgG1, IgG2, IgG3 and IgG4 were increased, the rank order being IgG1 > IgG2 > IgG3 = IgG4. Following treatment, a significant decrease in total IgG and the four subclasses occurred in the SAG-responsive group, whereas in the SAG-unresponsive group these levels were unchanged or slightly increased. Therefore, monitoring of IgG1 and IgG2 levels in Indian kala-azar patients is a good serologic alternative to monitoring the disease status.