To determine the lowest dose required preventing elastomer rejection, we added 0.025, 0.05, 0.75 or 1.0 mg of tricaine methanesulphonate per 50 ml water buffered with 1 ml liquid sodium bicarbonate. The bath was approximately 5 cm deep, which was shallow enough to ensure that the pneumostome was clear of the liquid. A pipette was used continually to bathe the slug in the solution. We used five slugs for each trialgroup. In addition to these 20 slugs, we included a control group of ten slugs. The control group was not subjected to anaesthetic or marking treatment, but was placed in water buffered with 1 ml liquid sodium bicarbonate. All animals were randomly assigned to either the control or anaesthetic treatment. They were either placed in the buffered control or anaesthetizing treatment bath for 15 min at 228C. All doses of anaesthetic resulted in the animals relaxing without causing excessive mucus production. Preliminary tests were conducted to find suitable marking sites on the slugs. We attempted to inject the elastomer beneath the skin on the mantle; however, the skin in this area tended to tear easily. Further, if the injection was too deep it could puncture the body wall, potentially resulting in mortality. Our preliminary trials found that that the elastomer could be easily and consistently applied to the translucent tissue of the foot, with minimal skin tearing and high visibility. Immediately following anaesthesia, we implanted visible elastomers (VIEs; Northwest Marine Technology, Shaw Island, Washington) into the 20 relaxed slugs. The elastomer was prepared by mixing 10 parts of the coloured component with 1 part curing agent as directed by Northwest Marine Technology. The elastomer-filled needle was inserted at a low angle into the translucent tissue on the outside edge of the foot. A very small amount of elastomer was then injected, resulting in