The main objective of the study was to investigate the effect of permeation enhancers and application of low frequency (LUS) and high frequency ultrasound (HUS) on testosterone (TS) transdermal permeation after application of testosterone solid lipid microparticles (SLM). SLM formulations contained 10% compritol and 5 mg TS /g of SLM. The permeation experiments were performed using Franz diffusion cells and abdomen rat skin. The examined permeation enhancers were 1% oleic acid (OA) or 1 % dodecylamine (DA). HUS (1 MHz) was applied in a continuous mode for 1h at intensity 0.5 W/cm(2). Different intensities and application time of pulsed LUS (20 kHz) were also examined. Additionally, the effect of combination of US and OA or DA was investigated. Skin irritation and histological changes were also evaluated. The results revealed that SLMs have an occlusive effect on the skin. Statistical analysis revealed the following order for the permeation of TS: 1% DA for 30 min>HUS +1% DA for 30 min= HUS=HUS + SLM containing 1% OA> SLM containing 1% OA=control. At total application time of LUS 6, 12, and 15 min the flux increased by 1.86, 4.63, and 4.77 fold, respectively. The enhancement effect of different intensities of LUS was not directly proportional to the magnitude of intensity. Skin exposure to HUS or LUS before application of 1% DA for 30 min had no superior enhancement effect over application of either LUS or HUS alone. Application of drug loaded SLM offered skin protection against the irritation effect produced by TS and 1% DA. Histological characteristics of the skin were affected to various extents by application of enhancers or ultrasound. In general, application of LUS gave higher TS permeation than HUS. However, safe application of LUS should be practiced by careful selection of exposure parameters.