AbstractWe measured the intrinsic viscosity of very small synthetic DNA molecules, of 20–395 base pairs, and incorporated them in a nearly complete picture for the whole span of molecular weights reported in the literature to date. A major transition is observed at M ∼ 2 × 106. It is found that in the range of ∼ 7 × 103 ≤ M ≤ 2 × 106, the intrinsic viscosity scales as [η] ∼ M1.05, suggesting that short DNA chains are not as rigid as generally thought. The corresponding scaling for the range of 2 × 106 ≤ M ≤ 8 × 1010 is [η] ∼ M0.69. A comparison of our results with existing equations, for much narrower data distributions, is made, and the agreement is very satisfactory considering the huge range of data analyzed here. Experimental concerns such as the effect of ionic strength, polydispersity, temperature, and shear rate are discussed in detail. Some issues concerning the Huggins coefficient, polymer chain stiffness, and the relationship between the Mark–Houwink constants K, α are also presented; it is found that log K = 1.156 − 6.19α. © 2011 Wiley Periodicals, Inc. Biopolymers 95:824–832, 2011.