Abstract. The stratigraphic distribution of the planktonic foraminiferal species Globorotalia margaritae has been determined in 34 DSDP, ODP and piston core sites from throughout the world’s oceans and from one land section. All these sites have good palaeomagnetic records, and thus the age of the first and last appearance of G. margaritae can be determined in each case. The results show strong diachronism and indicate that this is not a good species to use for correlation. There appears to be no simple explanation for this diachronism, dissolution is probably a contributing factor in the deeper sites, and the edges of the geographical range of the species show shorter stratigraphic ranges but these factors do not explain all the data. We suggest that diachronism in planktonic foraminifera may be common, but without global arrays of palaeomagnetically dated cores it will be very difficult to distinguish reliable species from unreliable ones.