Transmission blocked by drug resistance Resistance to the antimalarial drug atovaquone might prove to be this parasite's weak spot. Resistance develops rapidly via mutations in the drug's target: the parasite's mitochondrial cytochrome b complex. Goodman et al. have discovered that although resistant Plasmodium berghei parasites persist in mice, in blood-sucking malarial mosquitoes, the mutations disable female parasites too much for them to reproduce. The human-specific Plasmodium falciparum can only be investigated experimentally in mosquitoes, but a similar effect was seen. Thus, atovaquone-resistant parasites cannot be transmitted to another mammal or person. Science , this issue p. 349