We used the two long-term in vitro -adapted parasites 3D7 and HB3. The 3D7 clone was originally derived from NF54 parasites isolated from a Dutch girl near Amsterdam airport (5) . It was chosen here because it can be selected for expression of VSA PAM that react with PAM1·4 but not PAM8·1 (3). HB3 was cloned from the Honduras I/CDC parasite strain (6) , and was chosen because it can be selected for expression of VSA PAM reactive with PAM1·4 and PAM8·1. All parasites were grown in 0 + erythrocytes as described (3) .