A study was carried out at Central Institute of Agricultural Engineering, Bhopal, India to measure heart rate and oxygen consumption rate of six male operators during rotatilling and rotapuddling operations by a 6Γ7 kW rotary power tiller. Another set of experiments was conducted to measure the physiological responses while the operators walked alone on a puddled field. Physiological responses were measured under actual field conditions using an ambulatory metabolic measurement system. The data were collected at three levels of forward speed obtained in three low-speed gears at about three-quarters of the rated engine speed (1500 min Γ1 ). Physiological responses during rotatilling and rotapuddling operations varied linearly with forward speed. During the rotatilling operation, the mean values of heart rate and oxygen consumption rate were 97, 103 and 110 beats min Γ1 and 0Γ48, 0Γ58 and 0Γ63 l min Γ1 at forward speeds 0Γ30, 0Γ47 and 0Γ63 m s Γ1 , respectively. The corresponding values during rotapuddling operation were 101, 109 and 119 beats min Γ1 and 0Γ56, 0Γ70 and 0Γ86 l min Γ1 . Mean values of heart rate and oxygen consumption rate while the operators walked alone on puddled field were 99, 105 and 112 beats min Γ1 and 0Γ54, 0Γ63 and 0Γ75 l min Γ1 at the above forward speeds. The mean values for human energy expenditure were 10Γ02, 12Γ11 and 13Γ15 kJ min Γ1 during rotatilling, 11Γ69, 14Γ62 and 17Γ96 kJ min Γ1 during rotapuddling and 11Γ28, 13Γ15 and 15Γ66 kJ min Γ1 during walking alone on puddled field at the forward speeds of 0Γ30, 0Γ47 and 0Γ63 m s Γ1 , respectively. The study indicated that rotapuddling involved higher energy expenditure to an extent of 17-37% as compared with rotatilling for the above range of forward speeds. Walking alone on the puddled field was observed as a very strenuous activity, which required about 87-96% of total energy expenditure during the rotapuddling operation. Overall discomfort ratings on a 10-point visual analogue discomfort scale for 15 min work duration were 1Γ5, 2Γ6 and 4Γ1 during rotatilling, 3Γ3, 4Γ7 and 6Γ0 during rotapuddling and 3Γ4, 4Γ8 and 5Γ7 during walking alone on the puddled field at forward speeds 0Γ30, 0Γ47 and 0Γ63 m s Γ1 , respectively. Considering the physiological responses and the overall discomfort rating data as well as work output of man-machine system, it is recommended to operate the power tiller at a forward speed of 0Γ63 m s Γ1 during rotatilling operation and at a speed of 0Γ47 m s Γ1 during rotapuddling operation.