The enthalpies of interaction of N,N,N′,N′‐tetramethylethylenediamine (TMEDA) with poly‐(isoprenyl)lithium and poly(styryl)lithium were measured as a function of R ([base]/[Li]) by using high‐dilution solution calorimetry at 25°C. Both polymeric organolithiums exhibit initial exothermic enthalpies of interaction with TMEDA (R ≃ 0.1) of ca. −13 kcal/mole. The concentration dependencies show a break (decrease) in the plot of ΔH vs. R at ca. R = 0.5 for poly(isoprenyl)lithium and at ca. R = 1.0 for poly(styryl)lithium.