Haematological and biochemical parameters were studied prospectively in 48 dogs naturally infected with Angiostrongylus vasorum in a primary care setting. Samples for analysis were obtained when treatment was started and 42days afterwards. Prior to treatment, 21% of affected dogs exhibited eosinophilia, whereas increased total white blood cell (WBC) counts and neutrophilia were observed in only 4.2%. WBC counts and concentrations of neutrophils, eosinophils and monocytes decreased significantly from days 0 to 42, indicating that, even in dogs without elevated absolute blood values, a low grade inflammatory response may be present in dogs with A. vasorum infection. Biochemical changes (especially an increase in serum globulins and a decrease in serum fructosamine) were in agreement with the findings of other studies. The results show that the diagnosis of canine angiostrongylosis should not be excluded based on unremarkable haematological and blood biochemical parameters. They also support our recent finding that a low serum fructosamine concentration may be associated with infection with A. vasorum.