Amphibians are in decline in many parts of the world. Long time-series of amphibian populations are necessary to distinguish declines from the often strong £uctuations observed in natural populations. Time-series may also help to understand the causes of these declines.We analysed 23-28-year long time-series of the frog Rana temporaria. Only one of the three studied populations showed a negative trend which was probably caused by the introduction of ¢sh. Two populations appeared to be density regulated. Rainfall
had no obvious e¡ect on the population fluctuations. Whereas long-term studies of amphibian populations are valuable to document population declines, most are too short to reveal those factors that govern population dynamics or cause amphibian populations to decline.