In many fish species of which males care for eggs in a nest, including Aidablennius sphynx, females prefer to mate with males that already guard eggs. In this paper we present two aquarium experiments with this Mediterranean blenny to determine whether the females actually use the presence of eggs as a cue or depend on male display behaviour signalling the presence of eggs. In experiment 1 the test-female was presented with two nests, one with eggs and one without eggs, and only one male in a closed container between the two nests. This male only served to stimulate the female. In all tests females preferred to lay eggs in the nest already containing eggs. This shows that females of this species can base their choice on the presence of the eggs alone. In experiment 2 the test-female was presented with two males in nests of which only one had eggs. Transparent partitions deprived the female of the opportunity to inspect the nest contents. The male with and the male without eggs did not differ in time spent displaying towards the female, and the female did not show a preference for either male, based on visual cues or odours. After removal of the partitions the female visited both nests. The nest she visited first was equally likely to be the nest without eggs as the nest with eggs. In contrast, the female finally deposited eggs preferentially in the nest with eggs. We conclude that in this experiment females did not base their preference for males with eggs on male behaviour, but on the nest contents after inspection. This does not exclude an influence of male behaviour under other conditions. Furthermore, females generally deposit their eggs adjacent to as many as possible of the eggs already present, suggesting that females can localize and possibly estimate the amount of eggs already present.