Medicinal remedies of herbal origin employed by Criollos herdsmen of northwestern Chaco were studied through collections of plant specimens and by interviewing 83 local informants from several villages. A total of 619 medicinal uses were recorded for 163 plant species during field work. For each plant species the scientific and vernacular names, the parts of the plant used, specific medicinal uses, modes of preparation and administration and way of obtaining them were listed. Most species are collected in the wild (78%), they account for the seventy nine percent of the total recorded medicinal uses; the rest are obtained through cultivation or bought in markets. Plants are used mainly for diseases of the digestive tract (26.5% of total uses); skin affections (14.6%); respiratory disorders (9.1%); reproductive disorders (8.4%) and affections of the circulatory system (7.7%); and as antipyretics (7.5% of total uses).