One thousand and two hundred fifty seven blood samples were taken from persons coming from different zones of Costa Rica, in order to investigate phenotype and genotype distribution under the Kell system. Sample size was determined with the formula n= Z2pq/d² and allelic frequency by the gene counting method. The study reveals a phenotypical frequencyof 0,16% for K+ k-, 96,74% for K- k+ and 3,16% for K+ k+. These values correspond to a gene frecuency of 0,0171 for K and 0,9829 for k. These frecuencias were compared with the expected distribution applying a "Goodness of Fit" test. With two degrees of freedom, the X² value is 10,5970 (p<0,005), indicating that there was no statiscally significant difference between the expected and observed distribution. The founded values indicate that this system has a litle clinic and forensic significance in this country.

Kell System; Kell phenotypes; Kell genotypes; Kell genes Costa Rica