This research analyzes non-linear interdependencies between the Polish (WIG20) and the Spanish (IBEX 35) stock market returns with some other relevant international stock market returns, such as the German (DAX-30), the British (FTSE-100), the American (S&P 500) and the Chinese (SSE Composite) stock markets. In addition, this research focuses on the impact of the stage of the economy on these interdependencies, in concrete, on the influence of the 2008 Global Financial Crisis. To that end, we use a nonlinear autoregressive distributed lag (NARDL) approach in the sample period between January 1998 to December 2018. Our results show positive interdependencies between the Polish and the Spanish stock markets with the international reference stock markets analyzed in this research, as well as significant long-run relations between most of the stock markets. Furthermore, the Polish and the Spanish stock market returns may similarly react to positive and negative changes in international stock market returns, evidencing strong short-run asymmetry. In addition, both countries show great persistence in response to both positive and negative changes in stock market returns in the other mayor international markets. Finally, the NARDL model proposed in this research would show good explanatory power, mainly to changes in the international stock market returns, except for the Chinese market.