Four old-field loblolly pine (Pinustaeda L.) plantations of equal age and original spacing on sites of average quality in the Hilly Coastal Plain of Alabama, U.S.A., were sampled. Dry weights and nitrogen contents of all plant biomass components were estimated, including roots, to a 0.61-m depth. Soil nitrogen was estimated to the same depth. Dry weights and nitrogen contents per tree were comparable with those of earlier studies if allowance was made for different season of sampling. Estimated total aboveground mean annual accumulations of biomass and nitrogen 13 years after planting were 8100 kg/ha and 21.4 kg/ha, respectively. Trees comprise 84% of the plant mass and contained 61% of the N associated with plant tissue. However, the N content of the system's plant biomass was only 13% of the total; the remaining 87% was in the soil. Total-tree harvesting, even with stump extraction, would remove only about 7% of the ecosystem's nitrogen. Per hectare estimates obtained in the study differed considerably from some earlier estimates, indicating the need for additional studies in stands of different ages on sites of varying quality.