This study has developed and evaluated two instruments, a questionnaire, the Grief Diagnostic Instrument, and an interview, the Grief Diagnostic Interview to detect and measure the extant state of grief in general practice patients. These instruments investigate grief from past, present and impending death and non-death related losses occurring directly to the patient, as well as caused indirectly through experiencing grief in sympathy with the grief of others. The unique feature of these instruments is that they investigate grief from all losses rather than merely a single loss. The questionnaire was demonstrated to be a concise, valid, reliable and sensitive measure, and acceptable to general practice patients. It is suitable for epidemiological studies to detect a broad range of losses and to investigate the prevalence and severity of grief in general practice patients. It is also suitable for comparing the course and severity of grief between losses and identifying commonalities and differences. The interview was found to be an acceptable and valid instrument for undertaking clinical studies. Suggestions for further evaluation of the instruments, and for their uses in grief research and as clinical tools have been proposed. The findings that 2/3 of the general practice population studied were experiencing loss and that over 1/4 of all subjects were suffering moderate or severe grief, demonstrate grief to be a previously unrecognised significant mental health issue for general practice. The most frequently encountered loss categories were 'quality of life', 'death', 'separation' and 'job'. Non-death related losses accounted for 4/5 of all the losses detected. The lack of recognition of grief by subjects was demonstrated, particularly relating to migration and relocation. The hypothesis that loss and grief are under diagnosed and under treated in general practice is supported. This indicates the need for a new paradigm of loss and grief in general practice and for large-scale studies to investigate grief in general practice patients and the detection rate by general practitioners.