ABSTRACT In a cross-sectional survey of 187 Gambian children and adults, we have analyzed prevalence, fine specificity, and 19-kilodalton merozoite surface protein 1 (MSP-1 ₁₉ )-specific erythrocyte invasion inhibitory activity of antibodies to MSP-1 ₁₉ but find no significant association between any of these parameters and prevalence or density of malarial parasitemia, except that, after correcting for total anti-MSP-1 ₁₉ antibody levels, individuals with anti-MSP-1 ₁₉ antibodies that compete with an invasion inhibitory monoclonal antibody (12.10) were significantly less likely to have malaria infections with densities of ≥1,000 parasites/μl than were individuals without such antibodies. This association persisted after correction for age and ethnic origin.