The main object of this study is to determine the drying behaviour and conditions of shelled and unshelled pistachio samples using both solar assisted and open sun drying. For each drying experiment, 100 g each of unshelled and shelled pistachio were used. The least-squares method was applied to find the drying curve equation of pistachio. During the experiments, shelf temperatures, weight loss of pistachio, moisture content of air, and distribution of solar radiation were measured; and presented depending on the drying time. Also, the mass shrinkage ratios of shelled and unshelled pistachio samples were determined, and the experimental uncertainty ratio was calculated as 15-16.5 per cent based on the experimental results. It was deduced that the shelled and unshelled pistachio samples in the solar assisted forced convection dryer were perfectly dried at temperatures of 50 +/- 10 degreesC in the time period of 6 h. Whereas, the samples in the open sun drying were not sufficiently dried at temperatures of 28 +/- 4 degreesC in the same time period. Hence, it is suggested that the pistachio samples with approximately 29.0 per cent of moisture are dried in the solar assisted convection dryer at 50 +/- 10 degreesC of temperature in the time period of approximately 6 h in order to protect from the negative climatic and environmental effects. However, it is not desirable to dry the pistachio samples in the open sun because of greater drying time, dirt, dust and harmful insects. Copyright (C) 2001 John Wiley & Sons, Ltd.