This talk will discuss the paper "Relative regulators of number fields" by Friedman and Skoruppa. The relative regulator Reg(L/K) is essentially Reg(L)/Reg(K). Friedman and Skoruppa proved a lower bound for Reg(L/K) which is exponential in [L:Q]. Their method is to note that a certain relative theta-series in an increasing function, so its derivative is positive. This yields an inequality involving Reg(L/K). Estimating the other terms in this inequality, we obtain a lower bound for Reg(L/K).