A population of cells is said to be perfectly synchronised if all cells pass through the same point of their reproductive cycle at the same time, asynchronous if the percentage of cells in each phase of the cycle remains constant with time. These theoretically precise definitions, however, can seldom be applied in biological experiments, where researchers usually have to deal with partially synchronised or not completely asynchronous cell populations. As a consequence biologists need to calculate the degree of synchronisation of a cell population starting from data obtained with common laboratory measures and they need to know how to control the synchronisa-tion process. We investigated the behaviour of partially synchronised populations using computer simulations. Different kinetic scenarios, characterised by the mean duration of GO, G1, S and G2M phases, by their variability, by cell cycle blocks, etc., were tried out to show the differences in the growth curve and in the percentages of cells in GO, G1, S and G2M phases, as measured by flow cytometry. The effects of intercell variability of transit times on cell population synchrony were investigated and the transit of cells through GO phase was seen to induce an efficient loss of synchrony.