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In-vivo as well as in-vitro studies were carried out at regular intervals from 1979 to 1988 to monitor chloroquine resistance in P. falciparum in Bokajan and Manja PHC of Karbi Anglong district, Assam. The results showed no significant change in resistance status in the area. Intensified antivector measures, withdrawal of chloroquine pressure and prompt detection and treatment of P. falciparum cases with alternative drugs helped bring down the higher grades of resistant parasites by 1984, which however could not be maintained. The results of in-vitro tests correlated well with those of in-vivo tests. The Karbis seemed to have better immunity against the strain of P. falciparum than the non-Karbis residing in the area. However, there was no difference in the rate of sensitive and resistant cases detected amongst the two groups.

Studies conducted in Mizoram during 1981 to 1990 have shown areas with increasing RIII level of chloroquine resistance. These foci need urgent liquidation. Sulfalene-pyrimethamine drug combination was found suitable for treatment of P. falciparum cases in these areas with only 5.3 per cent cases showing RI level of Plasmodium response. Quinine combined with sulfalene-pyrimethamine showed 100 per cent success. Amodiaquine however was similar in response to chloroquine though the mean parasite clearance time with amodiaquine was slightly better.

In vivo test for the susceptibility of Plasmodium falciparum to chloroquine was carried out in 390 patients. Parasite density was analysed by calculating the mean of each day's parasite count and the value was expressed per microliters of blood. Majority of sensitive and resistant infections attained minimal values on day 4. Further more, this value provides a clear-cut, statistically significant difference between sensitive and RI cases (Z = 2.14, P less than 0.05) RII, RIII cases (Z = 3.86, P less than 0.001). It is proposed that assessment of sensitivity should be based on D-4 parasite density per microliters of blood considering D-0 as base i.e., (proportionate reduction of parasite density on D-4 as compared to that on D-0) utilising the present criterion. In endemic areas, where reinfection is possible, patency on D-14 will nearly always be due to resistance. It is therefore, suggested that a better, more economical and an epidemiologically viable result can be obtained by extension of in vivo test upto D-14.