The species Eucalyptus camaldulensis Dehnh. is of great importance in Mediterranean, sub-tropical and tropical countries for the production of domestic products, such as poles, posts timber and fuelwood. Some members of the genus Eucalyptus are reported to form both arbuscular- (AM) and ecto-mycorrhizas (EM). The main objectives of this study were to look at the host-symbiont interactions between E. Camaldulensis and AM and EM fungi, and interactions between the two mycorrhizal types. The initial aim of the project was to determine suitable experimental conditions for the formation of both types of mycorrhizas on E. camaldulensis seedlings. Two experiments, the first with AM fungi and the second with EM fungi, were set up successively using vermiculite-peat (VP) and sand-perlite (SP) as growth media, and 10 mg 1^-1 and 30 mg l^-1 phosphorus (P) Ingestad's nutrient solution in each case. Glomus intraradices Schenck and Smith. isolate UT 143-2 and Pisolithus tinctorius (Pers.) Coker and Crouch isolate PTE were used as the test AM and EM fungus respectively. Results showed that both AM and EM colonisation were very low (1-6%) but even so AM inoculation had a significantly depressive growth effect on seedlings of E. camaldulensis. In both experiments VP was found to be the best medium for both the growth of seedlings and the formation of mycorrhizas. A subsequent experiment using one nutrient concentration (5 mg 1^-1 P) and three AM and six EM isolates with VP as the growth medium resulted in colonisation of up to 20% by two AM fungi (Glomus clarum Nicolson and Schenck. isolate BR148-1 and Gigaspora rosea Nicholson and Schenck isolate FL105-5) but none of the EM fungi used in that experiment formed any mycorrhizas. The fourth experiment using three AM inocula (including two from the previous experiment and one from a trap culture of Bangladeshi soil) and four nutrient regimes (Ingestad's 2.5,5.0,10 and 20 mg 1^-1P) resulted in 30-50% colonisation; most colonisation was by G clarum BR148-1 and was greater at 10 mg 1^-1P (>50%). AM colonisation again resulted in a negative growth response of E. camaldulensis seedlings. In a similar experiment using five isolates of P. tinctorius, only isolate K55 resulted in colonisation >15% most of which occurred at 2.5 mg 1^-1 (>25%) while the other isolates resulted in <1% colonisation.