Observations of one D'-and five D-type symbiotic stars are presented: AS 201, He 2-106, He 2-127, He 2-171, AS 210, and Hen 1591. Several parameters are obtained for each object: interstellar reddening as determined from the Balmer decrement, considering optical depth effects; electron densities, estimated for adopted electron temperatures of 12,000 and 15,000 K; and helium abundances, also determined considering optical depth effects. Circumstellar contributions to reddening are estimated. The

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... positions and motions of these objects in a diagnostic diagram presented by the authors are shown and discussed.