Sensitivity of Plasmodium falciparum to chloroquine and sulfadoxine- pyrimethamine was tested among asymptomatic school children in 1995 and 1998 using a modified in vivo test with examination for parasitaemia on day 0, 2 and 7. Sensitivity (S/RI) to chloroquine in 'urban' areas was found in 42% in 1995 and 62% in 1998 with resistance at the RII/RIII level observed in 58 and 38%, respectively (P<0.01). In 'rural' areas, sensitivity to chloroquine was 76% in 1995 and 72% in 1998 (P = 0.6) with resistance at the RII/RIII level observed in 24 and 18%, respectively (P = 0.4). Sensitivity to sulfadoxine- pyrimethamine was found in 98 and 99% in 1995 and 1998, respectively. The apparent improvement in sensitivity to chloroquine in 'urban' areas might be due to a different school being included in the two studies. It is concluded that the pattern of sensitivity of P. falciparum to chloroquine and sulfadoxine-pyrimethamine has not changed over a period of 2.5 year. (C) 2000 Elsevier Science B.V.