In this study, a heat pump dryer was designed and produced in which drying air temperature was controlled with PID. PID controlled heat pump dryer was experimentally tested in drying tropical fruits such as kiwi, avocado and banana. Drying air temperature was kept at 40 degrees C with the accuracy of +/- 0.2 degrees C. Drying air velocity changed between 0.03 m/s and 0.39 m/s. Initial moisture contents of the kiwi, avocado and banana were 4.31, 1.51 and 4.71 g water/g dry matter, which were dried to 0.75, 0.35 and 0.5 g water/g dry matter moisture contents in 6 h. Afterwards the moisture ratios were analyzed with "STATGRAPHIC" computer program by using semi-theoretical models and empirical values. Correlation and standard error of estimation (SEE) and R-2 values were achieved. (C) 2007 Elsevier Ltd. All rights reserved.