The in situ stress field was determined, using the overcoring technique, at two underground sites at the Pea Ridge Mine, Sullivan, Missouri. At one of the stress sites in magnetite, the three-dimensional stress field showed the largest principal stress to be compressive (- 4,564 psi), nearly horizontal, and closely parallel to the strike of the orebody. The smallest principal stress was also compressive (- 2,047 psi) and nearly vertical. Considerable difficulty was experienced in drilling porphyry rock at the second test site in the host rock. Only one hole was drilled at this site. The secondary principal stresses obtained in the porphyry are--9,464 and -4,945 psi. The test site in magnetite is located at a depth of 2,505 feet; the site in porphyry rock is at 2,475 feet. The vertical stresses due to overburden loading at these sites are -3,590 and - 2,782 psi. Field determined values of the vertical stress are - 2,207 and -5,098 psi. The variance between the two sets of values is most likely attributable to the orebody formation and to the differences in the modulii of the host rock and the orebody.