In 1956, Lascelles was awarded a
Rockefeller Foundation fellowship, and went to
Stanford University for a year to work with
C. B. van Niel at the Hopkins Marine Station at
Pacific Grove, California. Van Niel was legendary in his knowledge of microorganism biology, and this experience afforded Lascelles a great deal, especially the ability to study more exotic bacterial organisms. She worked at dispelling the previously-thought rule that
anaerobes do not have
cytochromes, and the provision of a soluble
β-hydroxybutyrate dehydrogenase, which allowed
Krebs' group to devise a now widely used assay for
ketone bodies. In 1960, she was appointed University Lecturer in Microbiology at Oxford, a post she held until 1965. ==Professor at University of California==