REPORTS of Q fever in California in the 1940's called attention to the public health significance of the disease (1-3). Likewise, experiences of World War II demonstrated its military implications (4, 5). Q fever has consequently become a subject of investigation in many areas, military and civilian, both in this country and abroad. An important reason for the recent increases in Q fever surveys and research was the development of the Luoto capillary-agglutination test (CAT) as a rapid and reliable method for the serodiagnosis of Q fever in man and animals (6, 7). In addition, this technique provides an economically feasible method for conducting large-scale human and animal serologic surveys for evidence of Q fever infections. Naturally occurring Q fever in man and animals has recently been detected in a number of States previously presumed free of the disease (8-10). The nationwide occurrence of Q fever in dairy cattle has been reported (11). Available information indicates the disease is enzootic in most sections of the country with reservoirs in dairy cattle and sheep. Reports of sporadic human infections suggest the possible occurrence of endemic Q fever in some areas (10, 12). Relatively few reported studies have sought to identify and confirm human infections in recently recognized enzootic areas. Q fever in both animals and man was first reported in Iowa in 1957-58. Initial studies revealed that 0.7 percent of dairy cattle were serologically positive while 3.25 percent of dairy herds contained reactors (13). During this same period the first case of human Q fever in Iowa was identified (14). Subsequent studies (15) were conducted to investigate the epizootiology of the disease in dairy cattle, to confirm the infection status of serologically positive cattle by isolation of Coxiella burnetzi, and to evaluate the CAT method with milk samples as an epizootiologic tool (16). More recently, the prevalence of CAT positives among the human population of Iowa was investigated; a number of acute human infections were identified and subjected to detailed epidemiologic study. In addition, another survey of bovine serums was performed to detect any recent changes in the prevalence of bovine Q fever. This report presents the results of these studies.