Several studies have suggested a link between maintained cognitively stimulating activity and increased performance on cognitive tests in older adults.  However, the causal connection is not clearly established.  The current research seeks to provide experimental evidence to support the disuse hypothesis which suggests that some age-related cognitive decline may be attributable to reduced use of mental abilities.  We primarily focused on the effects of cognitively stimulating activity on age-related changes in fluid intelligence.  A sample of 44 older adults (mean age 67.12) was divided into two groups, each having a similar group-mean level of crystallised intelligence.  Both groups were tested (pre and post) on a battery of cognitive measures:  Raven's Standard Progressive Matrices, Alice Heim 4 II, Cattell's Culture Fair, WAIS-R Blocks and Digit Symbol Substitution Task, Trail Making Task A and B, and Digit Copying.  The experimental group was engaged in a 10-week period of increased, novel, cognitively stimulating activity involving both home and laboratory-based tasks and was compared to a control group who were tested pre- and post-test only.  Analysis showed a significantly greater increase in the experimental compared with the control group in pre- to post-test performance on two measures:  one the fluid measure 'Cattell's Culture Fair,' the other a measure of visuo-spatial construction, 'WAIS-R Blocks.'  Partial support for the hypothesis was obtained.  Future research will explore the durability and nature of the experimental effects observed.