Assorted cell line models including R2, PC43-10, RT16, D4, KB, and IGROV1 were assayed for [3H]MTX uptake as a measure of RFC levels and [3H]folic acid binding as a measure of FR levels. Assays were performed as described in the Experimental Section. For both transport and binding assays, radioactive substrate was expressed in units of pmol/mg protein. Abbreviation: FA, folic acid. Results are presented as mean values plus/minus SEM from 3 experiments.