Undergraduate nurses from the last four semesters of their course were interviewed about their understanding of the nature of pressure in relation to the use of some nursing devices, blood circulation and the measurement of pressure using a sphygmomanometer. The interview protocol was designed to be investigative during the first portion of the interview and to become instructive toward the latter portion of the interview. The study found that pre-service nurses significantly abbreviated the process of auscultatory blood pressure measurement as recommended in the nursing literature and that a number of them rounded-off manometer readings to the nearest ten millimetres of mercury. An analysis of interview transcripts revealed an array of differing concepts of pressure some of which impinged on the students' understanding of arterial blood pressure and the function of the sphygmomanometer. Despite the fact that many of the respondents did not understand the fluctuating nature of arterial blood pressure and the relationship between cuff air pressure and blood pressure in a functioning sphygmomanometer, most recognized blood pressure readings that were above the normal range and a number spontaneously gave advice regarding the blood pressure that they found. The implications for nurse education are discussed. [from publisher's website].