The increase in potential nutrient-absorbing surface area of loblolly pine (Pinus taeda L.) seedlings as a result of ectomycorrhizal development was quantified. In one experimental. In one experiment, loblolly pine seedlings were inoculated with Pisolithus tinctorius Pers. Coker (Pt) after having first been grown from seed for 8 wk under a low phosphorus (P) nutrient regime. Eight weeks following inoculation, seedlings were harvested and ail components of the nutrient absorbing system (including the fungal mycelium) were quantified. External mycelium accounted for only 5% of the potential absorbing-system dry weight, but this mycelium comprised 75% of the potential absorbing system area and over 99% of the absorbing length. In a second experiment, the P uptake and contribution to potential absorbing surface of Pt was compared to Cenococcum geophilum Fr. (Cg). Seedlings inoculated with Pt differed from those inoculated with Cg in that they (i) absorbed almost twice the P. (ii) had a higher frequency of fine-root branching, (iii) developed an extensive network of rhizomorphs, and (iv) had over 1.5 times the mycelial absorbing surface area and over 3 times the mycelial length of Cg. We conclude that for both Pt and Cg inoculated plants, external mycelium made by far the greatest contribution to the overall potential absorbing surface area of the pine seedling. Differences in total mycelial surface area and mycelial length may account for differences in P uptake between seedlings inoculated with Pt and those inoculated with Cg.