Transient, natural-convection pool boiling from spheres to subcooled sodium was studied. Hot tantalum spheres were submerged in sodium, and the surface temperature of the sphere was recorded, together with the pressure pulses which developed due to vapor growth and collapse. The experimental data were reduced by numerically solving the heat conduction equation in the sphere, the end result being the boiling curves of sodium. The following range of variables was investigated: sodium temperature—392 to 1607°F sphere temperature—2785 to 4281°F sphere diameters—1.0, 0.75, and 0.50 in. sodium depth—3.0 and 4.5 in. pressure—atmospheric . This investigation showed that sodium subcooling has a large effect on the transient boiling curve. The initial sphere temperature did not have an appreciable effect on the boiling curve as long as the initial regime was film boiling. An effect of changing the sphere diameter was observed only in the film boiling region. The experimental data in the film boiling region are correlated by ht = hƒb + 0.88 hr + Khc (Δ Tsc/ΔTS) , where h = heat transfer coefficient with subscripts t, ƒb, r, and c denoting total, film boiling, radiative, and convective, respectively Tsc and Ts = subcooled and saturation temperatures of the liquid K = 17.9/(ΔTSC)0.7, a constant depending on the degree of subcooling and sphere diameter. The experimental data in the film boiling region are correlated by ht = hƒb + 0.88 hr + Khc (Δ Tsc/ΔTS) , where h = heat transfer coefficient with subscripts t, ƒb, r, and c denoting total, film boiling, radiative, and convective, respectively Tsc and Ts = subcooled and saturation temperatures of the liquid K = 17.9/(ΔTSC)0.7, a constant depending on the degree of subcooling and sphere diameter. Both the minimum heat flux and the wall superheat at the Leidenfrost point are correlated by (q″)min = 6.3 × 104+ 1.9 × 103 ΔTsc ΔTmin = 7.9 × 102 + 12.2 ΔTsc ,  where (q″)min and ΔTmin are, respectively, the minimum values of the heat flux and of the temperature of the superheated liquid. In the transition region, violent interaction occurred. The degree of violence reached a maximum at sodium temperatures in the range of 1320 to 1570°F. Pressure pulses as high as 5.7 atm were measured at a distance 12 in. below the top of the sphere. The critical heat flux is correlated by (q″)crit,sc = 4.1 × 106 (1 + 7.8 × 10-3 ΔTsc) . Nucleate boiling data are presented in the transient boiling curves of sodium at various experimental conditions.