Gottfried sum from the ratio<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="italic">F</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mi mathvariant="italic">n</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math>/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="italic">F</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mi mathvariant="italic">p</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math>

Experimental results obtained at the CERN Super Proton Synchrotron on the structure-function ratio ${\mathit{F}}_{2}^{\mathit{n}}$/${\mathit{F}}_{2}^{\mathit{p}}$ in the kinematic range 0.004x0.8 and 0.4${\mathit{Q}}^{2}$190 ${\mathrm{GeV}}^{2}$, together with the structure function ${\mathit{F}}_{2}^{\mathit{d}}$ determined from a fit to published data, are used to derive the difference ${\mathit{F}}_{2}^{\mathit{p}}$(x)-${\mathit{F}}_{2}^{\mathit{n}}$(x). The value of the Gottfried sum F(${\mathit{F}}_{2}^{\mathit{p}}$-${\mathit{F}}_{2}^{\mathit{n}}$)dx/x=0.240\ifmmode\pm\else\textpm\fi{}0.016 is below the quark-parton-model expectation of 1/3.