(A) Comparisons of TSI₅₀ (•, TSI_{50, cont.}; ▴, TSI_{50, short}) values obtained by the use of [³H]-dUrd and [³H]-dCyd as substrates in the in situ TSIA. (B) Comparisons of TSI₅₀ values (•, TSI_cont.; ▴, TSI_short) obtained in fresh samples and after cryopreservation from 10 patients after 21 hours of continuous MTX incubation and after a 3-hour incubation period followed by an 18-hour drug-free period.