Size and survival rate of a population of Drosophila limbata in a cucumber greenhouse in the vicinity of Groningen, The Netherlands, were estimated twice in the summer of 1975 by mark-release-recapture experiments, using the Fisher-Ford model. The second time, an independent check was carried out by directly estimating the number of emergences. At the end of June, estimated population size was about 13,600, with a survival rate per day of 53.4%, at the end of July population size was estimated at 49,600, with a survival rate per day of 83.4%. The number of emergences per day was at the end of July 5,300, which is reasonably in line with the expectation from the mark-release-recapture experiment. At the end of June there was an excess of females, later there was an excess of males. Reliability of estimates, differences between estimates and growth of the population are discussed. Extrapolation from these data leads to an estimate of 3 million adult flies as the total maximum population size in the local area.