There is a lack of research documenting the weight-making practices of mixed-martial-arts (MMA) competitors. The purpose of the investigation was to quantify the magnitude and identify the methods of rapid weight loss (RWL) and rapid weight gain (RWG) in MMA athletes preparing for competition. Seven athletes (mean SD, age 24.6 +/- 3.5 yrs, body mass 69.9 +/- 5.7 kg, competitive experience 3.1 +/- 2.2 yrs) participated in a repeated-measures design. Measures of dietary intake, urinary hydration status, and body mass were recorded in the week preceding competition. Body mass decreased significantly (p <.0005) from baseline by 5.6 +/- 1.4 kg (8 1.8%). During the RWG period (32 1 hr) body mass increased significantly (p <.001) by 7.4 2.8 kg (11.7 4.7%), exceeding RWL. Mean energy and carbohydrate intake were 3176 +/- 482 kcal.day(-1) and 471 +/- 124 g.day(-1), respectively. At the official weigh-in 57% of athletes were dehydrated (1033 +/- 19 mOsmol"kg-') and the remaining 43% were severely dehydrated (1267 +/- 47 mOsmol . kg(-1)). Athletes reported using harmful dehydration-based RWL strategies, including sauna (43%) and training in plastic suits (43%). Results demonstrated RWG greater than RWL, this is a novel finding and may be attributable to the 32 hr duration from weigh-in till competition. The observed magnitude of RWL and strategies used are comparable to those which have previously resulted in fatalities. Rule changes which make RWL impractical should be implemented with immediate effect to ensure the health, safety and wellbeing of competitors.