Abstract Plasmodium falciparum contains a family of 21-base-long repetitive DNA sequences in its genome. A 21-base synthetic DNA oligomer, formerly labelled with phosphorus-32 for autoradiographic detection of P falciparum DNA, was covalently coupled to alkaline phosphatase for histochemical detection. The conjugate (PFR1-AP) detected purified P falciparum DNA with a sensitivity and specificity equal to that of 32P-labelled probes after 2-day exposures. PFR1-AP did not detect host DNA or DNA of other Plasmodium species. In African blood specimens PFR1-AP specifically detected P falciparuminfections of 100 parasites/μl. This sensitive, rapid, nonisotopic probe will allow more widespread use of DNA hybridisation in the diagnosis of malaria.