The resistance to airflow of bulk pistachio nuts (Ohadi variety) was determined using a laboratory unit in the range of 4.08-38.40% (w.b.) of moisture content, 0.08-1.00 m(3)/s m(2) airflow rate, 0-100 cm of bed depth and two fill methods. Three models (Shedd, Hukill and Ives, and Ergun equations) were investigated to describe pressure drop data of pistachio nuts. The pressure drop through the bulk pistachio nuts increased with an increase in airflow rate. bed depth, moisture content and bulk density. An increase in the moisture content range of 4.08-38.40% (w.b.) resulted in about 55% increase in pressure drop. The dense fill caused an increase in pressure drop by about 97% than that of loose fill. Shedd model was found to be the best equation to describe airflow resistance of pistachio nuts. (c) 2008 Elsevier Ltd. All rights reserved.