This is a brief report of preliminary results of the assessment of the correlation between baseline viral drug susceptibility and virological response in patients receiving mega-HAART. A total of 37 patients received > or = 6 drugs with a median follow-up of 8 months. There was evidence of extensive loss of viral drug susceptibility at baseline among the 24 patients analysed. Results showed that the magnitude and duration of virological response was associated with phenotypic viral drug resistance, although resistance did not lead to virological failure in all cases, and susceptibility did not lead to response in all cases.