An ultra low range turbidimeter with a measurement range from 0 to 1.0 NTU, in increments of 0.01 mNTU is described. The instrument utilizes a visible laser diode for its light source and a very sensitive detector, in a conventional nephelometric configuration, to achieve instrument sensitivity two orders of magnitude higher than is possible with traditional trubidimeters. Comparisons are made between the response of new instrument and two turbidimeters, one complying to United States EPA 180.1 and the other based on ISO 7027, to different sized Polystyrene Latex Sphere (PLS) samples. Includes 2 references, figures.