According to UNAIDS there were 34 million people living with human immunodeficiency virus (HIV) infection at the end of 2010. HIV is the causative agent of acquired immunodeficiency syndrome (AIDS) and the number of people dying of AIDS-related causes at the end of 2010 was 1.8 million. Due to the high mutability of the virus, there is a constant need for new approaches to attack the virus. Splicing of HIV-1 pre-mRNA is a highly regulated process. In order to produce all mRNAs needed to be infectious HIV-1 utilizes alternative splicing ­- from one single transcript more than 35 differently spliced mRNAs can be produced. A new approach to fight HIV-1 could be to interfere with the essential splicing. In this thesis, I describe the regulation of HIV-1 pre-mRNA splicing. SR proteins are involved in the regulation of splicing, both in an early and a late stage. We find that the intracellular concentration of SR proteins is of great importance for HIV-1 to be able to produce the correct amounts of mRNAs. Variations in concentrations of SR proteins lead to big changes in the HIV-1 pre-mRNA splicing pattern. The functions of HIV-1 protein Vpr are diverse and it is essential in vivo. HIV-1 vpr mRNA 13a7 is partially spliced, containing an intron, and the regulation of it is not fully understood. We find that SRp55 and SRp75 induce the production of HIV-1 vpr mRNA 13a7 by inhibiting splice donor 3. We also conclude that this inhibition at least for SRp55 is due to an interaction with the viral RNA element GAR. In the presence of SRp55 we also see an increase in cytoplasmic amounts of intron containing vpr mRNA due to increased nuclear export. Our results show that SRp55 can have several functions in the regulation of HIV-1 splicing: by inhibiting splice donors and by facilitating the export of incompletely spliced mRNAs to the cytoplasm. In conclusion, this thesis describes SRp55 as a regulator of HIV-1 vpr mRNA, both in splicing as well as in nuclear export. These discoveries provide an insight into the regulation of HIV-1 mRNA processing.