The game of field hockey demands high levels of perceptual and physical skill to compete successfully in a dynamic and challenging environment. The impact of hydration status and hot enviromuental conditions on field hockey performance has not been extensively studied. The research presented in this thesis was undertaken to examine the physiological, perceptual and neuroendocrinological responses to total body water loss on performance of elite female field hockey players following sport-specific intermittent running in the heat. Study one (Chapter 4) highlighted the match-play demands of the modern game of field hockey. Players spent the majority of match-play engaged in low-intensity activity (90%), while high-intensity activities such as cruising, sprinting and lunging accounted for the remaining time. Due to the continuous substitutions rule, playing time was reduced to 49 ± 13 mill, within which, 960 ± 272 motion changes occurred. From this motion analysis data and the utilisation of Global Positioning Satellite technology (GPS; Study 2, Chapter 5) during international matches (unpublished observations), a controlled laboratory-based motorised treadmill protocol (FHITP), designed to simulate the activity pattern observed during field hockey match-play, was devised and established as reliable (Study 3, Chapter 6). The fourth study (Chapter 7) was designed to investigate the hydration habits of elite female field hockey players. During consecutive competitive field hockey matches, body mass changes ranging from +2.4% to -2.0% were observed. There was a trend to suggest that some participants were not adequately replacing fluid deficits after matches as changes in pre- and post-match body mass (P = 0.028) and pre-match urine osmolality (P = 0.008) became significant in match two. Thus, the impact of mild dehydration on key components of field hockey performance were investigated in study five and six (Chapters 8 and 9). Study five (Chapter 8) demonstrated that ad libitum water ingestion was sufficient to improve visuo-motor perfoiTnance. In addition, dehydration impaired serial working memory performance, with greater deficits occurring when the task demands were complex and when the FHITP was performed in hot enviromrxental conditions (33°C, 60% rh; P < 0.01). Hot enviromnental conditions improved visuo-motor and simple working memory perfonuance. However, when the task complexity increased, working memory performance was impaired in the heat. In the sixth study (Chapter 9) a decline in field hockey skill performance and decision-making time in elite female field hoekey players was evident with ~ 2% hypohydration, despite no changes in rectal temperature, heart rate, sweat rate and blood lactate response. Data presented within the cuiTent thesis demonstrated that elite female field hockey players were susceptible to dehydration, which was of sufficient magnitude to impair both cognitive and skill performance.