The growth and survival of post-larval abalone Haliotis iris (mean initial shell length 570 μm) fed on eight strains (seven species) of benthic diatom were examined in the laboratory. Post-larvae showed active feeding behaviour on all diatom strains. Two strains (Achnanthes longipes-1 and Nitzschia sp.) produced significantly faster growth (means 34-35 μm shell length per day) than the remaining six strains (means 11-17 μm/day). The two fast-growth strains were efficiently digested by post-larvae, with 93-94% of live cells ruptured during passage through the gut. Two of the remaining strains could not be ingested during the growth experiment because the cells were too large (A. longipes-2) or too strongly attached (Cocconeis pseudomarginata). For the other four strains (Navicula britannica, Nav. ramosissima, Navicula sp. and Nitzschia ovalis) most cells passed through the gut alive. Survival rate was highest on the two fast-growth strains, and survival was positively correlated with both growth rate (r=0.73, P<0.05) and digestion efficiency (r=0.80, P<0.05) of diatoms. The digestion efficiency of diatom strains appears to be an important factor determining their dietary value. Digestion efficiency can be influenced by diatom morphology, attachment strength, frustule strength and post-larval age/size. Isolation and use of digestible strains may improve hatchery culture of abalone.