This study was conducted with the view to preparing methods and concepts for biorhythmic status diagnosis for the purpose of widest possible unbiased assessment of the living conditions of free-ranging wildlife. The study had to be started by a comparison of three various methods which were thought to be potentially suitable for long-time automatic acquisition of behavioral parameters from free-ranging animals. (The storage-telemetry-system ETHOSYS®, using extracorporeal measuring collars, is capable of high-continuity, long-term recording of activity and feeding from big herbivores. The radio-telemetry-system VIENNA can be used for recording of heart rate, body temperature and activity of roe deer and red deer. The recorder of jaw movements called APEC is capable of measuring rest behaviour, feeding and rumination in dairy cattle.) The ETHOSYS® system was used on Przewalski horse under semi-reserve conditions and on enclosure-kept red deer in a one-year investigation of the time pattern of activity and feeding. Data collected on 1,498 days were recorded from four Przewalski horses from June 1995 through July 1996. Data collected on 952 days were recorded from two red deer each between April 1995 and January 1996 as well as between July 1997 and May 1998. This study was conducted under more or less troublefree and quasi-natural conditions in order to provide species-specific standard values. The two species had in common for the whole year a polyphasic daily pattern with activity peaks at sunrise and sunset. The two behaviour parameters of either species were characterised by seasonal variations, a circadian rhythm and ultradian rhythms. In either species, change from predominant daytime activity to increased overnight activity in summer suggested response to heat or to molestation by flying insects. In Przewalski horse, annual activity and feeding levels were found to be separated from each other. Activity was at its highest in summer (70%) and lowest in winter (52%), but feeding was at its highest in autumn and spring(62%), with minimum values being recorded in summer (40%). In red deer, on the other hand, both activity and feeding had their lowest (winter, 25% for activity and 9 % for feeding) and highest (summer, 45% or 26%) values at one and the same time. In Przewalski horse, some of the seasonal variations in time patterns (total daily activity, relationship between daytime and overnight activities) occurred in a leapwise manner within one and the same week. In red deer, on the other hand, all seasonal variations in time patterns took a course of gradual transition. Species-specific season-related variations in nutrition, depending on nutritional conditions, led to variations in the ultradian structure of activity and feeding. Time patterns of activity and feeding in either species were characterised by 24-hour rhythmicity and by ultradian components of 4.8 to twelve hours in period length. Degrees of Functional Coupling (DFCs), a measure of harmony between internal rhythms and the external 24-hour period, were used to identify and evaluate irritative stimuli under usually quasi-natural conditions. Such DFCs helped to illustrate effects of various stress conditions and stress situations on time patterns of activity and feeding in various animal species (such as transport of a Przewalski horse from a zoological garden to our semi-reserve, hunting in short distance from positions of Przewalski horse and red deer, change in feeding regimes, removal of antlers from enclosure-kept red deer, social stress among red deer and alpaca individuals, lambing of mouflon and alpaca).