This paper investigates the impact of social media influencer endorsements on purchase intention, more specifically, the impact advertising disclosure and source credibility have in this process. The proposed framework argues that advertising disclosure has a significant impact on source credibility subdimensions of attractiveness, trustworthiness and expertise; subdimensions that positively influence consumer purchase intention. Empirical findings based on 306 German Instagram users between 18 and 34 years of age reveal that source attractiveness, source trustworthiness and source expertise significantly increase consumer purchase intention; whilst advertising disclosure indirectly influences consumer purchase intention by influencing source attractiveness. Furthermore, the results reveal that the number of followers positively influences source attractiveness, source trustworthiness as well as purchase intention. All in all, this paper makes a unique contribution to product endorsement literature, with evidence highlighting how social media influencers and advertising disclosure may be used on Instagram to effectively increase consumer purchase intention.