The performance studies of four different types of power threshers namely (i) Spiral thresher, made in Germany, (ii) Kyowa thresher, made in Japan, (iii) Marumiya automatic thresher, made in Japan and (iv) Axial power thresher, made in Bangladesh by Comilla Cooperative Karkhana (CCK), were tested in the Bangladesh Agricultural University Farm. All the four machines were tested for determining the labour, power and machine performances for wheat threshing. Each thresher was run for several hours with three different feeding rates. During each test, samples of threshed grain, straw and chaff were taken from their respective outlets for determining the parameters under study. MC = (Ww-Wd) / Ww × 100 ..... (1); where MC = moisture content in wet basis, % Ww = weight of wet grain, g Wd = weight of oven dried grain, g. The grain straw ratio was calculated as follows : K= Wd / Ws..... (2) where Ws = Weight of dry straw, g. The internal broken seed was identified by looking a seed over the light of a torch. A balance was used for measuring the amount of throughputs, straw and grains. The threshing efficiency, throughput capacity, material capacity, labour performance, power performance were calculated by using the following formulae : (a) Threshing efficiency (%) = G / (G + U) ×100 ...... (3); (b) Throughput capacity, Ct (kg/hr) = M / t ..... (4); (),(c) Material capacity, Cm (kg/hr) = G / t... (5); (d) Labor performance, PL1 (hr/kg) = 1 / Cm..... (6); (e) Labor performance, PL2 (man - hr/kg) = L / Cm ...... (7) (f) Labor performance, PL2 (kg /man - hr) = Cm / L ...... (8) (g) Power performance, Pp (hp - hr / kg) = hp / Cm ....... (9), where, t = time, hr; G = total amount of threshed grain, kg; U = total amount of unthreshed grain, kg; M = total amount of materials fed into thresher, kg; L = total number of labor required. The fuel consumption was recorded during each run for calculating the operating cost of the thresher. The cost of threshing was calculated by using the following formula : Chr = [{(FC x P) / A} + (RMP + L + F + O)] ...... (10); Ckg = [Chr / Tg ] ...... (11); where Chr = cost of threshing in Tk./hr, P = purchase price of the thresher, Tk., FC = fixed cost, 0.15P, Tk/yr, A = annual use of thresher, hr/year, RMP = repair and maintenance payment, ( 0.02% of P), Tk./hr, L = labor cost, Tk./man-hr, F = fuel cost, Tk./hr, O = oil cost, 30% of fuel cost in Tk./hr, Tg = weight of total threshed grain in kg/hr, Ckg = cost of threshing in Tk./kg. The cylinder speed was measured at least 5 times during each test by a tachometer and averaged to set the mean cylinder speed.