More and more Trojan asteroids are discovered in our Solar system, suggesting that they are probably a common spinoff of planet formation and evolution. Till date we know thousands of Trojan followers of Jupiter, and Trojan asteroids and moons of other major planets have also been discovered. The large number of such celestial bodies can mean that Trojan companions to extrasolar planets may also be common. Trojan celestial bodies are examples for the Lagrangian triangular solutions of the three-body problem. In this paper, the stability of the Lagrangian point L4 is investigated in the elliptic restricted three-body problem by using Floquet's theory. Stable and unstable domains are determined in the parameter plane of the mass parameter and the eccentricity by computing the characteristic exponents. Frequencies of motion around L4 have been determined both in the stable and unstable domains, and fitting functions for the frequencies are derived depending on the mass parameter and the eccentricity. Resonances between the frequencies are studied in the whole parameter plane. It is shown that the 1:1 resonances are not restricted only to single curves but extend to the whole unstable domain. In the unstable domains, longer escape times of the test particle from the neighbourhood of L4 are related to certain resonances, but changing the parameters the same resonances may lead to faster escape.© 2014 The Authors.Published by Oxford University Press on behalf of the Royal Astronomical Society.