Marine mollusk shells from various oceans and seas were analysed for their concentration of 10Be by accelerator mass spectrometry (AMS) and of 09Be by inductively coupled plasma atomic emission spectrometry (ICPAES). The ratio 10Be/9Be varied appreciably for different shells, indicating strong dependence on local conditions. However, the lowest ratio was measured in a Pleiocene shell from Italy, consistent with its age of 2.5 to 3 million years.