Circadian rhythmicity, an intrinsic characteristic of some physiological parameters in livestock, may be influenced by different exogenous synchronizers. The aim of the present study was to evaluate the influence of environmental temperature on the circadian pattern of some hormonal, haematochemical, urinary and physiological parameters in Alpaca (Lama pacos). For this purpose, 6 clinically healthy adult female alpacas aged 7 +/- 1 years and bred under similar conditions on a farm 400 meters above sea level were used. Twice, at two different environmental temperatures (5-13.5 degrees C vs. 11.5-33.5 degrees C), blood samples were collected by means of a jugular puncture and urine samples were collected by means permanent catheters on each subject every 2 h during 24 h. A trigonometric statistic model has been applied to the records' mean values obtained during the experimental sessions to describe analytically the periodic phenomenon; furthermore, the singles Cosinor method was applied to the periodic parameters. The application of the periodic model enabled us to point out the circadian pattern of the following blood parameters: Melatonin, glucose, triglycerides, urea, phosphorus, magnesium and potassium. The same model was applied to the following urinary and physiological parameters: Creatinine, magnesium, sodium, fractional clearance of magnesium and potassiumand body temperature. Rhythm stability and periodicity keeping under natural environmental conditions (characterized by variable temperature, relative humidity and photoperiod), though with different acrophases, enable us to establish that periodical parameters pattern shows a strong rhythm. This one can be influenced by exogenous factors (daylength and temperature in this particular instance) able to modify its synchronicity but not its intrinsic periodicity.