The purpose of this study was to examine the relationship between mean arterial pressure (MAP) readings, measured at two reference points, the right atrium (RA) and the catheter site (CS), and in two body positions, supine and semi-Fowler's. Four MAP readings were taken on 29 CCU patients, 17 males and 12 females, with ages ranging from 33 to 93 (X = 57.8; SD = 14.3). MAPs were obtained in the semi-Fowler's position-RA reference point (X = 82.6), semi-Fowler's-CS reference point (X = 90.3), supine-RA reference point (X = 82.2), and supine- CS reference point (X = 84.03). All r values for pairs of readings were greater than.90 (p < .001); therefore the readings are extremely comparable. However, when the comparability of readings is taken into account with MANOVA, the Hotel- ling's T2is 58.06; the associated F is 17.97 (df = 3,26) with p < .001. Therefore, in stable patients, MAP readings are comparable, but use of RA as the reference point for either position is the most preferable. A patient would not have to be lowered to the supine position for each MAP reading. However, in patients who are not stable, the significant differences among MAPs must be considered. The same position and the RA is preferable for all MAPs on these patients.