The transmission of light through a subwavelength hole drilled in a metallic thin .lm is calculated by numerically solving Maxwell's equations both for a simple hole and for a hole with additional structure. A maximum in the transmission cross section is observed for hole diameters of the order of but smaller than the wavelength. Transmission cross sections well above the hole area are shown to be attainable by filing the hole with a high-index material. The effect of adding a small particle inside the hole is also analyzed.