Hypersensitivity pneumonitis or extrinsic allergic alveolitis can be defined as a lung disease caused by a wide group of antigens that reach the lung by inhalation of organic and/or inorganic dust of various sources. The esparto (Stipa Tenacissima and Ligeum Spartum) is an herbaceous of the grass family used in the production of ropes, canvas, sandals, mats, baskets, and so forth. It is also used in the construction industry for the production of paper paste. Inhalation of esparto dust has been reported as cause of hypersensitivity pneumonitis. The existence of precipitating antibodies against esparto extract has been proved. During the esparto fiber manufacturing process, esparto grass can be contaminated by moulds and thermophilic actinomycetes, which have been described as the causing antigens of hypersensitivity pneumonitis in plaster workers. We present a case of occupational hypersensitivity pneumonitis in a plaster worker. Clinical findings, precipitating antibodies, and evolution, after having removed him from his work, confirmed the diagnosis. In our case, Aspergillus species contaminating esparto are probably the antigens that caused the disease.