A research programme in parasitology was conducted over several seasons, investigating several different organisms in the McMurdo Sound region. In the 1973-74 season, a study of the parasite burden of individual Weddell seals was conducted and samples for ultra structural studies were collected. Intestines taken from seal pups and their mothers from the Turtle Rock area were examined. Seals were ... also killed in the Pressure Ridge area adjacent to Scott Base and samples were collected for electron microscope studies. The small intestines of each of the seven seals were examined. In the 1975-76 seasons, the programme was aimed at examining some of the host-parasite relationships between helminthes, fish and certain invertebrates from the plankton in an endeavour to complete some cestode life histories. Three fish species were examined including Pagothenia borchgrevinki, Trematomus bernacchii and T. loenbergii. Quantitative data on all these parasites was recorded, while host material and parasite specimens were preserved for further examination. In the 1976-77 field season the study was continued with examination of various marine and terrestrial hosts with a view to completing life cycles of helminthes and in vitro studies on larval parasite growth. Glandicephalus perfoliatus, a tapeworm, was found in the bile duct of the Weddell seal and was analysed for ultra structural and histochemical properties. As assessment of the effect this parasite is having on the host tissue was also undertaken. The detailed study of the parasite burdens from the nototheniid fish of McMurdo Sound was continued. A new study was initiated using the difficult in vitro techniques to stimulate plerocercoid larvae from fish to mature into the adult tapeworm. In the 1977-78 season, a more detailed study of the plankton and bottom dwelling invertebrates was investigated to establish the hosts of the cestode procercoid stage. Fish stomach contents were used for this investigation and results were written in an initial report submitted to Antarctica New Zealand. An in vitro study of the plerocercoid and procercoid stages was conducted. Attempts at defining the conditions necessary for initiating growth and differentiation of adult Diphyllobothrium spp from plerocercoids in vitro was successful. The results of this work gave some idea of the length of viability of the cultures, the types of media and the percentages and types of serum in the media. Several parameters were tested: Pre-treatment, volume, sectioning of plerocercoids into 2 halves, monophasic and diphasic media, increasing surface area of solid base in diphasic cultures, changing the serum used in the solid base, different media, gas phase, size of plerocercoids and pH. The success of cultures was assessed by general appearance and growth of organisms. A study of the factors affecting the embryonation of tapeworm eggs released from cestodes in Weddell seals failed to embryonate any eggs. Samples were fixed for subsequent examination.