Proguanil (p.o.; 2.9 mg/kg body weight; daily for 5 days and 6 weeks respectively) shows mild degenerative changes for five days, while shows severe degenerative changes for six weeks in wistar strain albino rats. Serum testosterone level is significantly decreased for proguanil treatment rats. Administration of Malarone (Atovaquone and Proguanil) to experimentally B. gibsoni infected two dogs in chronic stage and three dogs in acute stage results in decrease in parasitemia, and clinical improvements are observed.