Balb/c mice were inoculated with live or inactivated organisms of Coxiella burnetii, strain Nine Mile, phase I. Sera collected after different time intervals were subjected to immunoblot analysis and results compared with ELISA values. Immunoblots were performed with different horseradish peroxidase labelled conjugates (goat anti-mouse IgG1, IgG2a, IgG2b, IgG3) and results monitored and analysed by laser densitometry. ELISA analysis was performed using the same peroxidase labelled goat anti-mouse subclass antibody conjugates. In addition, goat anti-mouse IgG(H+L), IgG(H), IgM, and IgA conjugates were used for ELISA tests.