The physical properties of cowpea seed were evaluated as a function of moisture content. The average length, width and thickness were 9.92 mm, 6.87 mm and 6.06 mm, respectively, at 12.01% d.b. moisture content. In the moisture range from 12.01% to 38.90% dry basis (d.b.), studies on rewetted cowpea seed showed that 1000 seed mass increased from 209.23 g to 256.88 g, the projected area from 22.59 to 32.72 mm(2), the sphericity from 0.781 to 0.799, the porosity from 50.64% to 51.49% and the terminal velocity from 9.31 m s(-1) to 9.61 m s(-1). The static coefficient of friction of cowpea seed increased the linearly against surfaces of four structural materials, namely, rubber (0.364-0.394), aluminium (0.212-0.296), stainless steel (0.176-0.238) and galvanised iron (0.324-0.36) as the moisture content increased from 12.01% to 38.90% d.b. The bulk density decreased from 569.9 to 535.6 kg m(-3) and the true density from 1154.8 to 1104.1 kg m(-3), respectively, with an increase in moisture content from 12.01% to 39.90% d.b. (c) 2006 Elsevier Ltd. All rights reserved.