The first survey of glucose-6-phosphate dehydrogenase (G6PD) deficiency and the Duffy blood group was carried out in connection with a malariometric survey in the rainy season of November 1986 in Republic of Guatemala. In 1, 510 persons, 28 patients with Plasmodium vivax and three patients with P. falciparum were found. The parasite rate was 2.1% in all age groups. The infant parasite rate was 1.2%. There was no significant difference in the parasite rates between the age groups whereas the parasite density was high in younger age group. The spleen rate in children under nine years old was 0.1%. In 567 males, three persons were found to be G6PD deficient (0.5%), but no person was G6PD deficient in 943 females. Six hundred persons were examined for the Duffy blood group : 85.0% were Duffy positive and 15.0% were Duffy negative. All the patients infected with P. vivax were Duffy positive, which was statistically significant (p<0.025).