Abstract: A method of and apparatus for collecting samples from a flowing stream in which an elongated sampling device including inner and outer concentric, relatively rotatable tubular members is positioned in and extends across the stream. The tubular members each have a longitudinally extending slot at least as long as the transverse width of the stream, with the slots being wider, and preferably at least about three times wider than the dimension of the largest particles contained in the stream. To take a sample, the inner tubular member is rotated to position its slot facing upstream, then the outer tubular member is rotated to position its slot in alignment with the slot in the inner tubular member to permit material from the stream to flow into the inner tubular simultaneously across the full width of the stream. When samples are not being taken, at least the outer tubular member is rotated to so that its slot faces downstream.