Energy costs and energy sources in karate (wado style) were studied in eight male practitioners (age 23.8 years, mass 72.3 kg, maximal oxygen consumption (VO2max) 36.8 ml.min-1.kg-1) performing six katas (formal, organized movement sequences) of increasing duration (from approximately 10 s to approximately 80 s). Oxygen consumption (VO2) was determined during pre-exercise rest, the exercise period and the first 270 s of recovery in five consecutive expired gas collections. A blood sample for lactate (la-) analysis was taken 5 min after the end of exercise. The overall amount of O2 consumed during the exercise and in the following recovery increased linearly with the duration of exercise (t) from approximately 1.51 (for t equal to 10.5 s (SD 1.6)) to approximately 5.8 l, for t equal to 81.5 s (SD 1.0). The energy release from la- production (VO2la-) calculated assuming that an increase of 1 mmol.l-1 la- corresponded to a VO2 of 3 mlO2.kg-1 was negligible for t equal to or less than 20 s and increased to 17.3 ml.kg-1 (la- = 5.8 mmol.l-1 above resting values) for t equal approximately to 80 s. The overall energy requirement (VO2eq) as given by the sum of VO2 and VO2la- was described by VO2eq = 0.87 + 0.071.t (n = 64; r2 = 0.91), where VO2eq is in litres and t in seconds. This equation shows that the metabolic power (VO2eq.t-1) for this karate style is very high: from approximately 9.5 l.min-1 for t equal to 10 s to approximately 4.9 l.min-1 for t equal to 80 s, i.e. from 3.5 to 1.8 times the subjects' VO2max. The fraction of VO2eq derived from the amount of O2 consumed during the exercise increased from 11% for t equal to 10 s to 41% for t equal to 80 s whereas VO2la- was negligible for t equal to or less than 20 s and increased to 13% for t equal to 80 s. The remaining fraction (from 90% for t equal to 10 s to 46% for t equal to 80 s), corresponding to the amount of O2 consumed in the recovery after exercise, is derived from anaerobic alactic sources, i.e. from net splitting of high energy phosphates during the exercise.