We report a new case of anti-Xg(a) antibody found in a man who, after receiving six units of standard red blood cells, developed a minor nonhemolytic transfusion reaction (chills-hyperthermia). The patient sera was used for an immunophenotyping scale in 777 healthy Tunisian blood donors (678 men; 99 women). The phenotype frequencies of Xg(a+) and Xg(a-) were 67.4% and 32.6% in men and 89 and 11% in women, respectively. The gene frequencies of Xg(a) and Xg were 0.67 and 0.33, respectively. These frequencies are similar to that reported in predominantly white populations.