Lipid spray beads (SB) were prepared containing 13% w/w particulate riboflavin. Beads suspended in seawater lost 73% riboflavin after 24 h. Release of riboflavin from SE ingested by Pacific oyster (Crassostrea gigas) larvae was observed under epifluorescent light. Riboflavin concentrations in tissues of adult oysters fed on riboflavin-SB were significantly (SNK, P < 0.05) greater than those of oysters fed on seawater-filled SE. Concentrations of riboflavin in oysters exposed to dissolved riboflavin were not significantly greater than those of oysters fed on seawater-filled SE: indicating that elevated riboflavin concentrations in oysters fed on riboflavin-SB were attributable to breakdown of ingested beads rather than uptake of dissolved riboflavin leaked from SE into the culture medium. SE seem to be a promising means of delivering water-soluble nutrients to bivalve suspension feeders.