Abstract: After blood inoculation with different doses of P. yoelii, the mice (Kunming strain) were found to be very susceptible. Even with 5 infected red blood cells, the infection rate of mice was 66.7%. But when inoculated with P. berghei in doses less than 1×106 infected red blood cells, only some mice were infected. Using similar doses, the para-sitaemia with P. berghei had a slower course than that with P. yoelii. After inoculation with P. yoelii, parasites disappeared naturally, but with P. berghei all the mice died soon after the peak parasitemia.