In order to evaluate clinically recognisable manifestations while undertaking examinations for fertility in cattle it is necessary to take cognizance of the physiological events taking place during the puerperium. The frequently incorrect diagnoses of cystic degeneration of the ovaries during this period can be avoided if the mechanisms controlling ovarian activity are properly understood. The close interaction between the ovaries, the hypothalamus, the hypophysis and adrenals as well as the luteolytic mechanism controlling ovarian activity is discussed. Attention is focussed on the effect of various pathogens on the endometrium, the influence of nutrition on the reproductive cycle and the consequent ovarian changes. The necessity to institute fertility examinations on a herd basis is stressed rather than attempts at treating the individual animal which, according to the owner, requires veterinary attention. By doing so a much more satisfactory service can be rendered. The existence of competent diagnostic centres, where the practitioner can obtain a metabolic or infection profile, is absolutely essential when fertility examinations on a herd basis are considered.