knowledge as well as high tech imports are included, case (3). However, in such a case, both **ai** and **_02_** are not significant. Case (5), which includes _TE_ and _SMHE,_ confirms these results. The strong relevance of high tech imports as vehicles of knowledge diffusion is confirmed in cases (6)-(9). This reinforces the impression that the regional effect of knowledge diffusion works mainly through imports rather than through other vehicles, as already found in Padoan (1996).

The case of the _UK,_ see table 4, presents rather weak regional effects and suggests that the role of foreign knowledge is much more relevant than that of high tech imports in knowledge diffusion. The value of **oi** -see case (1)- is significantly larger than that of **_02._** The same applies for high tech imports -see case (2)- but the associated elasticities are smaller and so is the adjustment speed. The goodness of fit is also less satisfactory. These results are confirmed by the other cases. Estimates including only one foreign variable, cases (7)-(10), confirm the results above. The UK is the only country case where all foreign variables, when included individually in the equation, are significant. This suggests that the pattern of foreign knowledge diffusion for the UK economy is both global (i.e. not strictly regional) and associated with different vehicles.

_Japan_ exhibits "regional" effects in technology diffusion, see table 5, in its linkages with the United States. However these are limited to the role of high tech imports as the stocks of foreign knowledge, both US and non US, are never significant, in accordance with results obtained in Padoan (1996). The point estimate of **_03_** is significantly higher than that of **_04,_** case (2). This is confirmed by the cases including only one foreign variable -cases (5)-(8)- where the cases including high tech imports from the US shows the best goodness of fit.

In conclusion, all countries show some regional effects of technology diffusion, although only Germany shows what we have defined a strong regional effect. It is interesting to note that, in the cases of France and the UK, regional effects are working through the foreign (European) stock of knowledge and not through high tech imports. Results for Germany and Italy, however, suggest that imports of high tech goods, rather than, or in addition to, other vehicles of knowledge diffusion reveal a regional pattern. The case of Japan also supports the role of trade as a vehicle of knowledge diffusion. Our evidence suggests that regional trade linkages represent only partially a factor of technological regionalism, a result partly at odds with those reported in the literature reviewed above. On the other hand, our results also support the view that vehicles of knowledge diffusion other than trade are relevant in regional linkages, a result that is not usually found in the literature.

# **4. Sectoral aspects**

In this section we consider sectoral aspects of technological diffusion in order to test whether technological specialization and diffusion is sector specific and whether the results obtained at the aggregate level hide a sectoral dimension. To this purpose we estimate a simple model which links trade and production specialization to technological specialization.

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