ABSTRACT: Efavirenz is a crystalline lipophilic solid with a low aqueous solubility and intrinsic dissolution rate. It is classified in class II of the Biopharmaceutics Classification System, which means it is poorly water-soluble and highly permeable. Spray drying is a widely used manufacturing process wich uses the aerosol phase to dry particles. By modifying the spray drying operation parameters, it is possible to control the properties of spray dried particles towards enhancement of drug bioavailability and delivery. Most studies use organic solvents but some of them have already been prepared as water based systems. We propose the use of water as solvent, since the use of organic solvents is increasingly contraindicated in pharmaceutical industry. The use of water, normally do not generate amorphous systems for low soluble drugs, increasing wettability and drug dissolution, do not leading to stability concerns. The results obtained demonstrate that co-spray-drying of EFV:SLS and EFV:PVP samples is an effective technique in the enhancement of efavirenz dissolution, in a process industrially viable. Different from results previously obtained with co-micronization, PVP was more effective than SLS in the dissolution enhancement of efavirenz when used co-spray-drying process. The characterization proved that the dissolution enhancement was not derived from drug amorphization and that there was any dangerous interaction between the drug and the carrier. Dissolution enhancement is probably related to the formation a hydrophilic layer in drug particles, inducing the interaction with the dissolution medium. The samples demonstrated potential to provide a better bioavailability based on the systems formed.