Sixty-nine children aged between 6 and 60 months with parasitologically proven Plasmodium falciparum malaria were treated with chloroquine (2.5 mg/kg) in the Children's Emergency Room of the University of Calabar Teaching Hospital (UCTH) in 1993. Thirty subjects (mean age 27.8 months) and 39 (mean age 29.5 months) received chloroquine phosphate suppository (Pharma Deko) and chloroquine sulphate syrup (May & Baker), respectively. The World Health Organization (WHO) 14-day in vivo field test was used in evaluating the response to treatment. In both treatment groups the responses were similar. Overall, parasitological cure occurred in 24 subjects (34.8%) and in the remaining 45 subjects (65.2%) treatment failed (chloroquine resistance). This level of chloroquine resistant Plasmodium falciparum (CRPF) is higher than 53.6% reported in this centre in 1989. Furthermore, in the present study the proportion of RII (46.4%) is significantly higher than 21.4% (P < 0.02) obtained in 1989. Our findings show a worsening of CRPF in Calabar with RII being the main contributor. This observation indicates the need for continued surveillance of the response of P. falciparum to chloroquine and alternative antimalarials as a means of evolving an effective treatment policy for malaria.