Extensive configuration interaction calculations have been done for the ground and first excited states of neutral lithium and singly ionized beryllium. While the calculations reproduce the ionization and excitation energies to within 3 cm−1 for Li and 10 cm−1 for Be+, the main purpose of this work is the accurate evaluation of the 2s–2p resonance line oscillator strength. The calculated value of 0.7478 agrees to within less than 1% with the very accurate laser excitation lifetime measurement of 0.7416 ± 0.0012. However, internal consistency checks of the accuracy of these calculations suggest that more precise calculations are unlikely to reduce this discrepancy significantly. Furthermore, when placed together with other independent calculations that should be of comparable, if not better, accuracy, all theoretical predictions strongly indicate an f-value of 0.7475 ± 0.0010, which differs from the experiment by 4 experimental standard deviations. Keywords: configuration interaction, correlation, oscillator strength.