Sampling is controlled to enhance analyte concentration estimation derived from noninvasive sampling. Means of assuring that the same tissue sample volume is repeatably sampled are presented, thus minimizing sampling errors due to mechanical tissue distortion, specular reflectance, and probe placement. In a first embodiment of the invention, sampling is controlled using automated delivery of a coupling fluid to a region between a tip of a sample probe and a tissue measurement site in a manner requiring minimal user interaction. In a second embodiment of the invention, sampling is controlled by controlling temperature variations, preferably with a coupling fluid, at a region about the tip of a sample probe and a sample site. In a third embodiment, sampling is procedurally controlled via timing and location of coupling fluid delivery to a sample site.