A direct method for measuring the resonance escape probability, p, in thorium-water lattices was experimentally examined. The system under investigation consisted of a square, close-packed, lattice of hollow aluminum clad thorium metal slugs (1.207 inch O.D., 0.495 inch I.D.) in. water, spaced to give a water to thorium ratio of 2 to 1 by volume (water to metal 1.45 to 1). A substitute lattice, in which the thorium was repla~ed by lead, was also used to give the same scattering properties as thorium but no resonance capture. The neutron source consisted of a fission plate made of a disc of U-235 (0.900 inch in diameter, 5 mgs in weight) mounted at the end of a Cd-covered aluminum tube which conducted a beam of neutrons from inside the thermal column of the VPI reactor into the lattice. Cd-covered indium foils were used to measure. flux traverses in two perpendicular directions, parallel to the slugs (denoted by II ) and perpendicular to the slugs (denoted by ⊥ ). 2 The curves of Ar² vs r, where A is the normalized relative activation of the foils, corrected for activation by epithermal neutrons from the primary source (reactor), were integrated to infinity and the ratio of the integrals in the thorium and lead lattices yielded p. It was found that p_⊥ and p₁₁ differed by only one percent, which was within the experimental error. It was therefore concluded that there was no anisotropy in the resonance absorption and the average of the two values, 0.88 ± 0.015, was taken as the value of p for the lattice. The experiment yielded also the age 𝛕 to indium resonance energy: In thorium lattice, 𝛕_⊥ = 44 ± 2 cm², 𝛕₁₁ = 46 ± 2 cm² In lead lattice, 𝛕_⊥ = 47 ± 2 cm², 𝛕₁₁ = 49 ± 2 cm² / Ph. D.