[en] Many solutions to the strong CP problem have been suggested in the literature, the most attractive one being due to Peccei and Quinn. The basic idea here is to impose an axial U(1) symmetry on the SU(3)_c x SU(2) x U(1) theory, such that there is an axial quark current A_μ that is conserved up to anomalies. A chiral rotation can then restore CP conservation. The way this symmetry was implemented in SU(3)_c x SU(2) x U(1), through two Higgs doublets, necessarily lead to a pseudo-Goldstone boson, called axion of mass f_πM_πM_W approx. 100 KeV and coupling to quarks approx. f_πM_W approx. 10^-₃. Such an axion was looked for but not found. Recently, Dine, Fischler and Srednicki (DFS) have suggested that a SU(2) x U(1) singlet Higgs transforming non trivially under U_PQ(1) and with a large expectation value renders the axion essentially invisible. If M_X is the expectation value of the singlet Higgs, mass of the axion M_a approx. f_πM_πM_X and pseudoscalar coupling approx. f_πM_X. In grandunified theories we can get fields with large expectation values, which can be singlets under SU(2) x U(1). The implementation of the DFS idea in grand unified theories is discussed