Sir,Despite the large amount of proteins in the plasma, the urine is virtually protein free due to the selectivity of the glomerular barrier [1]. The major component of urinary protein is a tubular protein (Tamm-Horsfall) while albumin constitutes 30–40% of the total urinary protein. Various physiologic settings, including exercise, can induce a transient increase in the urinary protein excretion that is usually benign and reversible. The type of post-exercise proteinuria depends on the intensity of exercise rather than its duration, so that moderate exercise induces glomerular and heavy exercise glomerular-tubular mixed-type protein loss [2]. Post-exercise proteinuria may be due to the loss of the charge selectivity from the glomerular capillary wall, a relative preservation of the glomerular filtration rate, proteinuria out of proportion of maximal tubular reabsorption capacity following heavy exercise [2,3] and oxidative stress produced by free radicals due to enhanced oxygen consumption in muscles [4]. The purpose of our study was to compare the amount and pattern of proteinuria before and after karate (Kumite) competition in 18 male practitioners, aged 18–21 years, with similar physical characteristics. All practitioners competed in three rounds, each lasted 3 min, with a 10 min resting interval between them. Urine samples were collected just before the competition and during 24 h thereafter. Total urinary protein, urinary beta2-microglobulin B2M as tubular and albumin as glomerular protein were assayed. Before competition, the mean value of total urinary protein, albumin and B2M as basal levels were 70.68 ± 12.5, 4.84 ± 3.17 and 0.0217 ± 0.0133 mg/day, respectively. After competition, the mean values of 24-h total urine protein (196.05 ± 70.88 mg/day), albumin (34.07 ± 32.88 mg/day) and B2M (0.0933 ± 0.0372 mg/day) levels were significantly increased (P = 0.023, P = 0.001 and P < 0.001). This study revealed significantly increased proteinuria of a mixed type (albumin and B2M) in all practitioners following exhaustive short-term competition. Despite the mixed type of proteinuria, we observed a six-fold increase compared to the basal level in urine albumin (versus four-fold increase for urinary B2M) suggesting a more prominent role of glomerular proteinuria probably due to glomerular membrane permeability changing factors, such as sympathetic overactivity and competitive stress.Conflict of interest statement. None.