Haploid plants were found in progenies of the following varieties of Coffea arabica : typica, bourbon, maragogipe, semperflorens, laurina, erecta, caturra and San Ramon. These haploids resemble the normal plants from which they have originated ; they are reduced in size, their branches are more slender and the leaves are narrower and thinner. Flowers are normal, smaller, with very low fertility, due to abnormal meiosis. The dominant genetic factors maragogipe (Mg), erecta (Er), caturra (Ct), and San Ramon, and the recessive factors semperflorens (sf) and laurina (lr) have the same phenotypical expression both in haploid and normal plants. The Br (bronze young leaves) gene shows incomplete dominance, the heterozygous plants having light bronze tips; the haploid with a single dose of Br has also a light bronze color of the young leaves. In the presence of tt the Na gene is incompletely dominant the heterozygotes having the murta phenotype (ttNana). Haploids derived from bourbon (ttNaNa), therefore hemizygotes t Na, do not resemble murta but bourbon. Attention was called to pure lines obtained through duplication of chromosome number of haploids, for use in progeny tests, in order to measure the environmental variation, and also to determine mutation rate in C. arabica. Observation on meiosis and the results of genetic analysis have already pointed out that C. arabica is probably an allotetraploid of ancient origin ; this has been confirmed by the study of the haploids here described. Monosperma coffee plants with 22 somatic chromosomes, and the bullata types with 66 or 88 chromoeomes, should not be considered any more as varieties of C. arabica, but only as haploids or polyploids of the varieties from which they originated.