The authors review the conditions concerning "Q" fever, both from the clinical and epidemiological point of view. The first national case was communicated in 1956, the affected subject being an adult worker from a meat processing plant. In 1966 the first case on a child was described. From then on, several serological surveys v/are carried out on human beings and on animals. Concerning human beings positive results ranked from 4.2% to 5.5%, depending on the year the study was made. In animals, the values rank from 0.9% (local consumption animals) to 30% (industrial type animals) as far as bovines are concerned. As for ovines, in the single study performed, a 10.3% rate of positive findings was reached. In horses, the positive finding rate ranked from 5.5% to 21.7%. A positive rate of 21.2% was the result of the first survey in swines. A more recent one showed 0.0%. Neither fowls nor guinea pigs showed positive sera. Between 1975 and 1985, 14 meat plant outbreaks were studied and the results showed that, of a total a 1358 human cases studied, 60% of them were positive. The patient's most common symptomatology and the nature of the task performed are also listed. Both for the serological studies and for the diagnosis of the clinical cases, the authors use the complement fixation, the capillar agglutination and the layer microagglutination. This last technique was previously described by the authors 21.