In this talk, I will present a method introduced in 2010 by Cristofol and Roques to obtain uniqueness results in inverse problems of determining non-constant coefficients of nonlinear parabolic equations. This method is mainly based on the Hopf's lemma and on the parabolic maximum principle. It can be applied to several types of 1D reaction-diffusion equations and systems, such as the Fisher-KPP equation and Lotka-Volterra competition systems.