The aim of this project was to modify transmission models previously developed to describe HIV transmission in Ireland through more precise estimates of parameters delineating sexual and needle sharing behaviour and AIDS related mortality, with a view to examining the extent of spread from IVDUs to the general heterosexual population. To provide predictions on HIV transmission and AIDS cases up to the year 2010 and to examine the sensitivity of the predictions to changes in the key parameters under different assumptions on intervention strategies. Essential data of relevance to HIV transmission were acquired (through the cooperation of the Department of Health, the AIDS Resource Centre, the Drug Treatment Centre, the Ana Liffey Drug Project, and St James’s Hospital, Dublin) and analysed. The parameters obtained from the descriptive and survival analyses were used in a refined deterministic model of HIV transmission which was solved numerically. An attempt at a solution using perturbation methods was undertaken. Results provided a plausible range of projected new HIV infections and AIDS cases up to the year 2010. The model projects that if present behaviour continues, approximately 1009 new infections may be expected in Dublin by the year 2000, and 1496 new infections by 2010. Small changes in the values of key parameters induce significant changes in projected trends, particularly in the longer term. However all projections point to the fact that •Non-IVDU women are particularly susceptible to HIV infection •Early introduction of behaviour change makes a significant difference to the growth of the epidemic •Expanding the Drug Treatment System could help to significantly reduce the spread of HIV •Central collation of data is essential if rational implementation of intervention plans is to be achieved