SUMMARY relevant epitope in the invasion process in vitro by the merozoite. This assay was a useful tool to evaluate in vitro protective Mabs implicated in the inhibition of invasion. Objective. Antibodies are glycoproteins that can protect against diseases like malaria by binding and neutralizing parasites. The effect of antibodies on surface proteins is to block invasion. In this work, we developed an assay to evaluate the inhibition of invasion of Plasmodium yoelii mediated by the Merozoite Surface Protein 1 (MSP-1), which is one of the invasive blood stages of the malaria parasite, using several Monoclonal Antibodies (Mabs) raised against a 19 kDa fraction of MSP-1 (MSP-1 19 ). Material and Methods. Mabs were previously evaluated in a passive transfer experiment which inhibited the growth of the parasite and were characterized. A panel of five of these Mabs (B10, B6, F5, D3 and D9) raised against the C-terminal fragment of MSP-1 from P yoelii were used to evaluate the inhibition of invasion. An ANOVA test was used to compare the inhibition effect. Results. The protective and partially protective Mabs were evaluated in a growth assay in vitro. The inhibition effect of invasion was determined as significant (p<0.05) for Mab F5. The results suggest that Mab F5, an IgG3 which recognizes the first epidermal growth factor (EGF)-like module of the fragment C-terminal of MSP-1 19 , can interfere with erythrocytes invasion in vitro, in the first 30 minutes of the invasion. Conclusions. This suggests that the first module of MSP-1 19 , which is recognized by Mab F5, is a